In a great story on the Lucasfilm acqusition by Disney in Bloomberg Businessweek, George Lucas more or less admits that Mark Hamill, Harrison Ford and Carrie Fisher are returning for the new movies:
Asked whether members of the original Star Wars cast will appear in Episode VII and if he called them before the deal closed to keep them informed, Lucas says, “We had already signed Mark and Carrie and Harrison—or we were pretty much in final stages of negotiation. So I called them to say, ‘Look, this is what’s going on.’ ” He pauses. “Maybe I’m not supposed to say that. I think they want to announce that with some big whoop-de-do, but we were negotiating with them.” Then he adds: “I won’t say whether the negotiations were successful or not.”
That may be the big news out of this, but the article itself is a must-read on the process, with extensive input from Lucas and Bob Iger.