Tell a story about the Rise of the New Jedi Order, or tell a story about how the Fall of the Empire gives way for some outside enemy that no one knew the Emperor was keeping at bay. But don't give me three movies about Luke, Han, and Leia playing Bridge with Chewbacca while sipping tea and reminiscing about their youth. Take a cue from Obi-Wan in ANH: He sacrifices himself so that the OT is about Luke, not some old dude who can't swing a saber anymore.
I don't think anybody is claiming that this new series is going to be about
Luke, Han, and Leia. Just because those characters are still alive doesn't mean the story is going to focus on them. If you have the opportunity to tell a new story AND bring back some beloved characters, I don't see why you wouldn't. The three of them were pretty instrumental in the fall of the Empire; it stands to reason they'd still be active in galactic politics.