Such as the new Rey film which could set up a storyline for SW going 'forward' perhaps instead of being a coda (apology?) for the sequel trilogy.
With Luke, Han and Leia gone they're kind of the last of the Original trilogy crew, although Luke could possibly appear as a force ghost.
There's a deleted ROS storyline about Lando's daughter being kidnapped years ago and indoctrinated into being a Stormtrooper by the first order and presumably Jannah and possibly Finn could help in that search given their own Stormtrooper pasts (Lucasfilm has made it pretty clear that Jannah isn't the daughter BTW). The Shadows of the Sith novel also went into this a bit (including that he was involved in hiding Rey, he just didn't know it? I haven't read the novel but I guess that happens.)
Chewbacca and R2 of course should be easy with many tall actors around for Chewie and R2 can be realized by electronics or a small actor most of the time, and their vocals are of course effects easy to replicate or already archived. but Anthony Daniels is getting up there in age. While 3PO is also a masked character, Daniels has pretty much been in costume or the voice 90% of the time including special events, ads etc. (Maybe he feels only he can do the proper body language of the character?)