I mean, if you wanted to end your revenge doesn't pay ending with a descent into insanity, maybe? I dunno, really the biggest problem with the original ending for me is letting Abby get away AFTER losing her fingers. It should have been a consequence of not backing down rather than a sunk cost. Sunk cost fallacies are fallacies, but people tend to believe in them anyways, and there really wasn't much else to lose if she didn't finish Abby off.