Of their position players, likely Reyes, maybe one or both Castros, and perhaps Jones, Demeritte, and Goodrum might survive to '21. I don't believe that Greiner, Candelario, Stewart, or Lugo will, unless say Stewart hangs on by being Mr. 26 if he demonstrates at least somewhat of an uptick in his offense this season. Jones MUST pick up where he left off, having successfully tweaked his batting mechanics, before sustaining a season-ending injury last year. ex-Royal and non-rostered ST invitee Frank Schwindel is 5 for 14 with a double, 2 homers, and a BB, but he is strictly a DH/1B, and the Tigers have both positions covered with the contracts of Cabrera and Cron. He will likely be going to Toledo, with only a chance of being called up to the big club if either Miggy or CJ become injured...or later if Cron becomes trade bait and departs before the July deadline.
The Tigers utterly lack primetime-ready positional prospects, and of those in the minors, Paredes, Gibson, Cameron, Rogers, Clemens, Deatherage, ect...any would need to have truly breakout and injury-free seasons to get called up before the trade deadline and later roster expansion. (unless the team sustains a or some season-ending injury or injuries to a key positional player or players). Only Greene has truly distinguished himself so far, but he is very likely @ least another season away from getting his cuppa joe in the majors. Whoever they pick @ #1 prolly isn't gonna be the next Kaline, as far as being in the majors starting next season.
The Tigers rotation looks to be initially comprised of Matt Boyd, Spencer Turnbull, Daniel Norris, Jordan Zimmermann, and Ivan Nova....but it is conceivable that the Tigers could release Zimmerman, if he performs poorly enough, but he would need to REALLY suck, given Chrissy's propensity for squeezing every nickel out of his franchise. I have a feeling that Nova won't pitch very well for the team, and he might even surpass Zimmerbum on Tigers fans' shitlists.