I think Jack killed himself in the end. The guilt he feels for turning Anna into a monster and getting Grace in trouble is too much to bare. He wakes up in a field, both of the people he loves are there. It's not too long after what happened, probably within a few months since Jack's leg is still messed up from the incident. The two girls have sort of put the whole thing in their past, and have absolutely no scars to show of the incident. Grace even has her teeth back. This is exactly what heaven would be like for Jack, alone, sitting peacefully underneath a tree in a field with the two girls he loves the most. And do you really think Anna would have magically stopped being a psycho because Jack reveals that he never had a plan? That the most important thing to ever happen in her life wasn't planned, that it just happened for no reason? No, not after all that trauma. She had to bury the trauma of her parents death with the sheep and wolf story to begin with, the only thing that kept her going was believing that Jack was a hero, that he was a wolf. She wouldn't have been fine, she would have done something drastic. Not to mention Grace Anna kidnapped her and pulled her fucking teeth out. Anyway, that's my theory. Would love to hear what you guys have to say!