If he's not in Ep7, then they are going to need to use up value movie time to explain why. He was too important of a character in the OT to just brush him off.
It's easy enough to just put Mayhew in the make-up from the waist up and give him mostly white hair to show that he's aged. Then he can just send a transmission from his home-planet explaining why he can't be a part of the main storyline. Han can even make a comment on how his "life debt" had been paid off many times over and he told Chewie to go home and take care of his family.
Something like that would be better than to just say "Oh, he died. Go read read this book, now on sale at your local bookseller, to find out how."