Revisting characters?
Sylar has to be there. Has to.
Past that, I'm guessing perhaps Hiro, Claire, and Peter. Maybe Matt Parkman. Don't/shouldn't "need" anyone else 'ceptin' Claire's Dad, and that's iffy-ish unless he's some sort of Nick Fury-esqe leader.
Although that creepy dollmaster Eric Doyle would be pretty cool as a villain maybe.
Whatever, I'm in.