I'm intrigued by the concept that Vader's helmet survived the funeral pyre, (if indeed it's supposed to be that very helmet) and someone recovered it from Endor at some point. It's a cool Shakespearean way to have Vader in the movie.
Much to my amazement, the ROTJ funeral helmet does still exist.
http://thepropden.aokforums.com/funeral-pyre-vader-vt788.html