All the respect in the world to Manuwa. He started training martial arts very late in life, I think at 27, and still gave a pretty good account of himself at the top level in the sport. Had he started training in his teens with a respectable coach who could have shored up his defensive holes in his youth, the man might have been a world champion.
That said, I believe his time has passed. He should probably stay retired, although I wouldn't really have a problem with him taking a one off against a light puncher in England and going out on a win.