Deathstroke
Slade Wilson
My impression was that he stayed to figure out the truth, take revenge on Alex and stop the evil she was doing, not necessarily to find Moira alive and leave the island happily ever after. He even acknowledged at the beginning of his third chapter that he couldn't save Moira, but would do everything in his power to save Christmas Girl. So I don't think he actually believed in Moira's survival until he met her. But of course, that wouldn't stop him from hoping nevertheless.
Very well put.