So I've come across several discussions on different articles as to whether or not we will be seeing Hamill, Fisher, and Ford back to reprise their roles.
All I've heard is that it will be "an original story" so I'm not even sure if the casting would require that.
I have to say though, of the three, the only one I would really like to see back would be Mark Hamill. I think it would come across as very believable having him in the role of a wise Jedi mentor, considering how he's aged between now and then.
I can't wrap my mind around seeing Ford and Fischer back in any capacity. I'm just not sure where they could go with that. Yes, they both have aged as well, but to me it makes sense having Hamill back because of it. It would totally fit.
Unless they are planning on starting immediately after ROTJ....then I guess they would just recast everyone.