Yup, its possible he could be in it, he'd be older obviously but its something that has always been a question mark that could finally be officially resolved. Really all they need is a flashback sequence showing his escape.
I think now Disney own it he will get his own film at some point, be an instant cash flow for them.
Anyway onto this film i cant wait to see it, for the odd poor review its got it doesn't phase me i enjoyed force awakens too.
Im interested to see how darker this spin off is as the trailers make it appear that it has gone for a dark tone, I also hope Vader scene dont feel forced in