I don’t know, but it doesn’t seem like every contract needs to be redone. I could see if someone still has 6 months left (like Adrienne warren) that producers might want to hold the actor to that. But I assume actors could break the contract if scheduling conflicts with other projects. And then there is aging out of a character for certain parts might be an issue after a year and half off.
I have not seen any statement whether all contracts are redone or all roles recast for shows. I tend to think if a show is completely recast, the rehearsal period will be much longer than getting a few new actors up to speed.