I think Obi Wan would have said goodbye to Luke at some point after ROTJ, much like he did in Heir To The Empire. There's always the holocron/hologram angle which Rebels has already done.
Ewan might look good with proper old age makeup, unless they CGI footage of Sir Alec as was done with Brando in Superman Returns. They would still need Obi Wan to say lines Guinness never said in the OT, which puts J.J. in Frink's shoes. ;)
Seeing the Ewoks kick some ass would great! Luke could have asked them to guard the remains. And told Threepio to keep his vocabulator shut. ;)