Thanks man, the RP idea is genius btw.
I was thinking that he might possibly have kept the mirror, believing that it might be a way of getting revenge. The same deity that tormented him as a child could then come back and make him a deal: the lives of one of the good parties (perhaps that of Alex and Elsa) for the lives of his parents.

Basically, the deity gives him the location, he goes and gets his butt kicked by a superior breed of warriors. They then interrogate him, accidentally reveal their mission (stopping genocide). His fire for revenge overcomes his need for his parents... and after much dialogue and debate, he joins the quest.
I'm open to any other ideas, this is just a suggestion.