Here is what will happen and (in some cases) might happen after the conclusion of the World Series...
At 9 AM (Eastern) on the day after the final game of the World Series, the eight Cubs MLB Article XX-B free-agents (Jake Arrieta, Alex Avila, Wade Davis, Brian Duensing, Jon Jay, John Lackey, Rene Rivera, and Koji Uehara) will be declared free-agents (players do - NOT - have to file, it's done automatically) and will be removed from the Cubs MLB Reserve List (40-man roster) at that time.
Clubs retain exclusive negotiating rights with their own Article XX-B free-agents until 5 PM (Eastern) on the 5th day after the final game of the World Series (the first five days of free-agency are known as the "Quiet Period"), after-which the player can sign with any MLB club. Clubs also have until 5 PM (Eastern) on the 5th day after the final game of the World Series to decide whether to extend a Qualifying Offer to any of their Article XX-B free-agents who are eligible to receive one. (Lackey is not eligible to receive a Qualifying Offer post-2017 because he received a QO previously in his career, and Avila and Rivera are not eligible to receive a QO post-2017 because they were acquired by the Cubs during the MLB regular season). I suspect the Cubs will extend a QO to both Arrieta and W. Davis, in part so that the Cubs can receive draft pick compensation should the player sign with another MLB club, but also because the Cubs would actually want the player to accept the QO.
Players who receive a QO now have ten days to decide whether to accept (it used to be seven days). This gives the player ample time to receive contract offers from other clubs, and determine if the QO is maybe a better deal. If the player accepts the QO he receives a one-year guaranteed 2018 MLB Uniform Player Contract (UPC) for the 2018 QO salary ($17.4M) with no incentives or performance or signing bonuses. A player who accepts a QO is automatically and immediately returned to the club's MLB 40-man roster. Arrieta has already said there is no way he would accept a QO, but W. Davis possibly might.
W. Davis probably is looking for a contract similar to the one Mark Melancon signed with the Giants last off-season (four years - $62M - opt-out after two years), but the 2018 QO actually exceeds the AAV of Melancon's deal, and so W. Davis might possibly choose to accept the QO once he has had a chance to talk $$$ with other MLB clubs (after the five-day "quiet period"). I think the Cubs would love to get W. Davis back on a one-year deal (even for $17.4M), but would probably not be interested in a multi-year deal without club options allowing them to terminate early. A player opt-out after two years (like Melancon got in his deal) would probably be OK with the Cubs.
The Cubs also might offer catcher Rene Rivera a 2018 minor league contract for "big league money" (maybe as much as $3M) and an NRI to Spring Training, probably with the understanding the he will be added to the Cubs MLB 40-man roster (and MLB 25-man roster) prior to Opening Day. Because he will be an Article XX-B FA post-2017, Rivera would receive an automatic $100K retention bonus and a June 1st opt-out if he isn't added to the MLB 40-man roster by Opening Day. But by signing Rivera to a minor league contract, the Cubs would have an additional slot open on their 40-man roster throughout the off-season and Spring Training (up until Opening Day).
The Cubs could add RHRP Matt Carasiti (eligible to be a minor league second-contract FA) to their MLB Reserve List (40-man roster) by the deadline (5 PM Eastern on the 5th day after the final game of the World Series) just to keep him from walking away as a FA. Carasiti was the closer at AAA Iowa after being acquired from the Colorado Rockies for LHRP Zac Rosscup in June, and so he would be a definite candidate to win a job in the Cubs bullpen in 2018. The Cubs might be able to sign Carasiti to a 2018 minor league successor contract prior to the deadline, but then he becomes eligible for selection in the Rule 5 Draft, and he would be a good candidate to get plucked given his AAA experience and some MLB innings in 2016. So even if he signs a minor league successor contract, he still could get added to the Cubs MLB 40-man roster by the 11/20 roster filing deadline (as happened with Jack Leathersich last year, who signed a 2017 minor league successor contract in October, and then was subsequently added the 40 on 11/18 anyway).
So with eight slots open on their MLB 40-man roster after the World Series, the Cubs will likely add six minor league players to the 40, leaving two slots open for free-agents who might be signed prior to December 1st (this year's MLB contract tender date, moved-up one day because the usual contract tender date of December 2nd falls on a Saturday).
As things stand right now, the Cubs will probably add RHP Adbert Alzolay, INF David Bote, RHRP Matt Carasiti, and RHSP Oscar de la Cruz, plus two more from among Rule 5 Draft-eligibles RHRP Jake Stinnett, IF-OF Chesny Young, RHSP Trevor Clifton, LHP Jose Paulino, RHSP Erling Moreno, OF Charcer Burks, INF Jason Vosler, and RHRP Pedro Araujo, and minor league FA OF John Andreoli. (Stinnett, Young, and Clifton are probably the best bets right now, but how Stinnett, Burks, Vosler, and Araujo perform in the AFL could alter that projection).
There are two or three other players the Cubs will probably drop from their MLB 40-man roster on December 1st to open up additional off-season roster slots, those three being C-INF Taylor Davis and IF-OF Mike Freeman, and possibly OF Leonys Martin. The trio could be non-tendered on 12/1 and then the Cubs could try and re-sign the player(s) to a 2018 minor league contract (with an NRI to Spring Training) after the conclusion of the Rule 5 Draft (which will be held on December 14th).
While T. Davis and/or Freeman could get outrighted to the minors (presuming the player isn't claimed off waivers) within the next few days, T. Davis would be a minor league 6YFA if he is outrighted prior to 5 PM (Eastern) on the 5th day after the final game of the World Series - AND - he cannot be outrighted after that date & time unless and until he signs a 2018 contract (which are tendered on 12/1), and Freeman is an Article XX-D player (he has been outrighted previously in his career) and so he can elect free-agency if he is outrighted. And because they have Rule 6 Draft-Excluded Player status, neither T. Davis nor Freeman can be sent outright to the minors after November 10th (the last day of the current waiver period). They can be non-tendered on 12/1, however, but there is no guarantee that either would sign a minor league contract once he is non-tendered. The Cubs might try and work out a deal with T. Davis and/or Freeman in advance, otherwise they would lose the player as a FA with no compensation for the club (not even the waiver price) if the player signs elsewhere.
Martin will almost certainly be non-tendered, because otherwise he must be tendered a 2018 MLB UPC with a salary no lower than $3.88M (no more than a 20% cut from his 2017 salary of $4.85M), and I doubt that the Cubs would want to go there. Martin is also arbitration-eligible, and there is no way to predict how an arbitration panel might rule. (Martin could even get a raise above his 2017 $4.85M salary!). So by non-tendering him, the Cubs could (if the player agrees to the deal) sign Martin to a 2018 MLB contract with a substantially lower salary (perhaps somewhere around $1.5M), or (even more likely) sign him to a 2018 minor league contract (with an NRI to Spring Training), with a chance to make the Opening Day MLB roster as a 4th or 5th OF. Otherwise, Martin would be the CF at AAA Iowa. (Again, that's presuming Martin agrees to the arrangement).
The Cubs also might opt to non-tender Justin Grimm, Hector Rondon, and/or Justin Wilson (all three are eligible for salary arbitration), not to sign them to minor league contracts, but rather to offer the player a "custom contract" with a low base salary and a performance bonus (something the Cubs cannot do if the player is tendered a UPC) and to avoid the risk of salary arbitration.
For example, instead of tendering Rondon a standard non-guaranteed UPC with (let's say) a $6.25M salary (which is his projected salary if he opts to file for arbitration), the Cubs would offer Rondon a guaranteed "custom contract" with maybe a $3M base salary plus another $4M or so in performance bonuses based on games/appearances (so he'll make more money if he stays off the DL) and Games Finished (should he become the Cubs closer in 2018). Guaranteed 2018 MLB "custom contracts" with low base salaries plus incentives could be offered to Grimm and Wilson as well, but the Cubs would probably need to have deals in place prior to the contract tender deadline, because otherwise the player can just decline the offer and walk away as a FA and the Cubs get no compensation if the player subsequently signs elsewhere.
And then if they need still additional slots on their MLB 40-man roster during the off-season, the Cubs could try and sneak RHSP Luke Farrell, RHSP Alec Mills, and/or LHSP Rob Zastryzny through waivers (if outrighted, Farrell and Zastryzny would remain under club control through the 2019 season, and Mills would remain under club control through the 2018 season), but that probably would not be necessary. With eight Article XX-B free-agents leaving after the World Series and two or three more players likely to be non-tendered on 12/2, there should be four or five slots available for free-agents and waiver claims (and maybe even a Rule 5 Draft pick), even if six minor leaguers are added to the 40 prior to the Rule 5 Draft.
Also, remember that beginning this year, MLB Rule 4 Draft (First-Year Player Draft) Competitive Balance draft picks can be traded starting on December 2nd and continuing up until two hours prior to the Rule 4 Draft in June.
Previously Competitive Balance draft picks could only be traded during the MLB regular season.
So it's very possible that Competitive Balance draft picks could be dealt in trades made at the MLB Winter Meetings next month, or later in the off-season or during Spring Training.
Competitive Balance Draft picks can be traded only once (a pick cannot be flipped to a third team once it is traded), and (best of all) a Competitive Balance draft pick is - NOT - subject to forfeiture if a club signs one or more Article XX-B Qualified Players. (Prior to the new CBA, Competitive Balance draft picks were subject to forfeiture if a club signed an Article XX-B Qualified Player).
So let's say the Cubs sign an Article XX-B Qualified Player like ex-TB RHSP Alex Cobb and lose their 2nd round pick. The Cubs could get a pick back (maybe even a higher one) by acquiring a Competitive Balance draft pick as part of a trade.
14 MLB Clubs have 2018 Rule 4 Draft Competitive Balance picks, plus one of the 14 clubs (TB) has an additional comp pick as the result of failing to sign a 2017 Competetive Balance draft pick.
AFTER 1ST ROUND:
32. TB (comp pick for failing to sign #31 pick in 2017 draft))
AFTER 2ND ROUND:
A club might be interested in trading its Competitive Balance pick because the bonus slot value for some of the picks are in excess of $1M, and a club might prefer to acquire a young (cheaper) prospect with maybe a "higher floor" but also a "lower ceiling" who has already received his signing bonus and maybe shown some promise in the minors, instead of a draft pick that will cost the club a lot of money in terms of signing bonus and who has not yet played a pro game.
Cubs prospects who might have value to other clubs in a trade for a Competitive Balance draft pick while maybe not having that much value to the Cubs (given the Cubs MLB roster) could include guys like OF Mark Zagunis, LHP Rob Zastryzny, INF David Bote, OF Charcer Burks, RHP Alec Mills, OF Eddy Julio Martinez, IF-OF Chesny Young, and/or C-1B Ian Rice.
Also keep in mind that a trade involving a Competitive Balance draft pick does not have to be one player for a draft pick. It could be a two-for-one or three-for-one deal, or part of a much larger trade involving multiple players.