If he had simply lost, he would have had to come to terms with the death himself. Even the greatest magician was not able to defy fate.
By removing his memories it puts him in a place where there is no closure, and on top of that he now has a bunch of memories missing. Even if he were ignorant of his past, he definitely would question why he has such a big spot of his memory gone. Then again, assuming that a sorcerer who dicks around worlds has any sense of compassion is a lost cause.
It wouldn't surprise me if Morlock picked up and raised Raelza as a replacement for his daughter, because even with his memory gone the body and soul doesn't forget so easily.