Considering Disney has outright confirmed they will develop standalone Star Wars films to debut in between the numbered episodes, fans should definitely expect to see familiar characters back on the big screen in the years to come. Recent reports suggest that the spin off films could even center on main-line players like Yoda, Boba Fett, and a young Han Solo - making it all the more likely that we'll see several classic trilogy actors back (one way or another).
In the case of Han Solo, for example, an appearance by Harrison Ford in Episode 7 would definitely make that rumored standalone film feel a bit more essential to the larger canon. Instead of a one-off adventure (and shameless cash grab), the Han Solo spin-off could actually provide backstory that informs the character's actions as an older man in the new trilogy - even if the connections are very subtle. It's a move that would help sooth resistant fans - especially as Lucasfilm gets closer to casting a young Solo (assuming the rumors are true) - as well as draw in casual viewers, who might otherwise have skipped the standalone films. After all, it worked for The Avengers - why not Star Wars? Plus, that's before we talk about merchandising opportunities.