His brain is being hyjacked in a way that kills everything that is his person. He's being wiped of his personhood and replaced with a cannibalistic zombie that isn't him. Zombified people are no longer with us. Permanently completed NPCs are killed people. He's getting consumed by the death cult, and he's too deep in to be pulled out.

In some ways, it's more gruesome than a bullet because when he disappears, his body doesn't expire. It continues to walk as a monster hurting and potentially killing. As horrid as a bullet to the brain is, it doesn't do that.

If there's a chance he won't be permanently erased forever, it's easily basically nonexistant. I have to radically accept that he's gone for good.