Well my personal argument is you use him as a trade piece before you get to that point. Whether or not that's realistic or what will happen is obviously another story. I've made the comment here that I wondered if his promotion was done in order to give them a reference point on where he was. If you compare him and Bryant, Bryant had roughly 400 PAs between AFL and AA before a promotion to AAA. He obviously destroyed in those. I believe Baez had around 300 in AAA this year and really only played well in June and July which amounts for 200ish PAs. Bryant's 22 with the book on him being a great approach. Baez is 21 and the book on him is often over aggression. AAA to MLB is considered the hardest jump for a prospect. Arguably if you're not going to promote Bryant faster then why on earth would you promote Baez as fast as they did? And don't get me wrong I'm fine with the way they've handled Bryant but the contrast between the two seems off.
My wonder is if the cubs brought him up to see if that adjustment was a short one as it was with A+ and to an extent AAA or if it was going to be a long one. Keep in mind it took around 100 PAs to adjust to A+ and AAA before he was at least semi-useful. We're currently at 215 for Baez and the 100 PAs in September were actually worse than the 100 PAs he's had in August. As I've suggested with the numbers, it sure seems like he's 2 years away minimum from being a productive major league player. I can't really see a light turning on next year and suddenly Baez is a .270/.340/.550 hitter with 35 HRs. A more likely case for positive for him would be like .230-.240 hitter with adjust the other numbers accordingly. Then maybe the following year you get to that line and that's assuming he fixes his issues.
Given the wealth of MI prospects they have and given that time frame if you can package him for a core piece I don't see a reason not to. And when I say core piece, I'm talking someone on Rizzo's level of production as a hitter or roughly equivalent pitcher. And even if Baez does become a solid player I'm not sure you lose that trade if you get a Rizzo level piece. Since 1871 through present day there have been 11 players(two did it twice) to have seasons over 4 fWAR with over 27% k rate which would be a massive improvement on where Baez currently sits. Granted WAR isn't the end all be all stat but it's a very good catch all to contrast vastly different players. Those players are Chris Davis(2013 6.8 fWAR), Cecil Fielder(1990 6.5 fWAR), Jim Thome(2001 5.4 fWAR and 1999 4.2 fWAR), Jose Canseco(1990 5.2 fWAR), Mike Cameron(2002 5.1 fWAR and 2008 4 fWAR), Adam Dunn(2004 4.9 fWAR), Reggie Jackson(1968 4.7 fWAR), Jose Hernandez(2002 4.6 fWAR), B.J. Upton(2007 4.5 fWAR), Dan Uggla(2008 4.3 fWAR), and Colby Rasmus(2010 4 fWAR).
If you apply that father down to 3 WAR there's only been 26 individual seasons by players. So, even if Baez does end up over coming his issues it seems less likely that he'll ever be a star unless he vastly overcomes his strikeout issues. At 2-4 WAR he'd be by no means a bad player but hypothetically say you trade him and parts for someone like Matt Harvey who goes out and is a 4-6 fWAR pitcher per season. You almost surely end up with the best player in the deal unless the other pieces end up being quite good. So to me that's why I'd try to trade him this offseason. I think people should obviously be concerned with his debut but at the same time I think it hasn't killed his trade value yet. Obviously the right deal has to be available to make that work but I really don't see how you lose by trading him. I see almost no scenario where he gets under 27% career K rate barring a unexpected Bautista like turn. And if he never does, the chances of him being better than the player you trade him for are rather remote and you remove all of the risk in prospect development not to mention my concerns on Baez individually.
Like I said, it's probably unlikely to happen but that doesn't mean it's not logistically sound.