Michael, Linc, and Sara are safe. It would be incredibly lame to kill off Sara after bringing her back.
Mahone is going to go out in a blaze of glory getting vengeance or to redeem himself saving the others (or both). He doesn't even want to live any more except to live long enough to get revenge.
I think LJ and Sofia are pretty much safe. LJ being in trouble as a motivator has been overdone so they'll probably just be minor players this seasons.
T-Bag is such an important adversary and part of the humor of the show that I doubt he'll die, but he sure does have it coming. He'll find a way to survive in the end.
Bellick and Sucre do indeed provide comic relief, but they're also fairly expendable plot wise. Bellick dying probably wouldn't be a huge guilt trip on Michael like they always try to do, but Sucre would. So I wouldn't be surprised if one of them ended up dead.
Gretchen's got to die. Sara's going to kill her.
Asian hacker dude and the FBI agent just have dead man walking written all over them. FBI agent guy will die just when they think they've reached their moment of triumph in taking the Company down and the rug is pulled out from under them by killing the only FBI guy who knows what they're up to.