I get that he really seemed to like the Sox and enjoy his time in Chicago, but why would he want to come back and play under Pedro Boylen if (theoretically) those are his thoughts about the manager?
Jose Castro, Daryl Boston, and Chris Johnson were let go/left. I'd guess that Castro probably had more term on his deal considering he was one and done, but the Sox don't typically disclose that information for whatever reason.
I don't entirely discount having leaders in the clubhouse, I just take issue with bringing in bad and expensive baseball players to be "leaders" because they're someone the manager can point to and say "see he respects me so you should to too". I think a good chunk of the leadership problems can be pointed back at Pedro for being completely ineffective and not knowing how to do anything outside of being an ass-kisser.
Perez is a bad defender now, so going from old catcher that can't catch to slightly less old catcher that still can't catch BuT lEaDeRsHiP would be very on brand.