Harrison Ford is on record to come back to play Han, IF he gets a dead role to play. Mark Hamill and Carrie Fisher might be up for playing there roles too. It all depends on the story Disney is working on, and how far along they will take the story after the Jedi film. Even if it's only flash backs, would you like to see these 3 play a part in the next film?
IMO I think they should be there, and even if it's just this one film, it's a great way to kick it all off again.