They need to be mentors. Luke needs to take on the Ben Kenobi role for whoever the protagonist is. I'm not sure how I want Han and Leia to fit in. Maybe as people that the protagonist meets along their journey, similar to Nimoy in '09 Star Trek. Just people to provide exposition and context to the main character and move them along their journey. Also, I hate to say it, but I think Luke needs to die in either episode VII or episode VIII. You can't expect the protagonist to grow if their mentor hangs over their shoulder to give them advice throughout their entire journey. Obi-Wan, Gandalf, Morpheus: It's a popular and extremely effective plot device to have the mentor sacrifice themselves for the hero.