My Thoughts on Rogue One

Rumors are that various versions (acting, stunt etc) of Darth Vaders classic suit were seen on set, and of course there are the rumors that Hayden Christensen had met with the movies stunt choreographers, so I think its almost certain that Vader will return, possibly portrayed by Christensen.

oh god not Hayden Christensen

If Hayden were to return I wouldn't have any problem with it. He wouldn't even have a speaking role, as James Earl Jones would provide the voice.