I think under the right circumstances Hamill would come back for a film or even a trilogy. Let's say Christopher Nolan is directing a script from Frank Darabount and executive produced by George Lucas to the tune of $300 million per film, and it sounds like a really awesome movie/trilogy, and they are also going to pay him well; Hamill's already typecast and has no real career to guard against. That sort of attitude only made sense when he was younger and had the potential to take himself in more ambitious directions. He can still do his comic books and cartoon voice-over, too. But I think if the films were put together in an attractive package pretty much all of the original cast would be on board in a second, maybe even Ford too.