How about this idea. Excalibur shows that Juggy is slowly weakening. He wasn't a mutant, it was just the residual effect of the Ruby of Cyttorak slowly leaving his system. so Juggs leaves the team to search for a way to restore his old powers before he's completely human.
This gets him caught up in a world of sorcery and action as he is abducted by Cyttorak, who offers Cain the chance to be the Juggarnaut again, but at a steep price. he would have to give up all the redemption he's attained in the recent years, have to revert to criminal acts. So this is Cain trying to find the middle ground, so that he can regain the powers he grown so used to that he considers a part of himself, but not lose the new self. This of course would require he has someone to comeback home to, so I would suggest before he leaves the Excalibur, he start a romantic entanglement.