I don't think his redeeming qualities dissolved into anything. He was clearly motivated by the loss of most of his pack, and nothing happens over the course of the film that discredits this. In fact, the only particularly bad thing he tries to do is get his revenge by eating the pack leader's baby. Other than that, everything he does is standard villainy, if not completely normal predatory behavior, like trying to bring down Manny with the remaining members of his pack. It's perfectly normal for a pack of saber-tooth tigers to try taking down a mammoth, especially if they don't have many other food options due to many of the animals migrating south and whatnot, and he only tried to kill Diego after he explicitly turned on him. So all in all, he's largely just a a typical predator who wants revenge for his pack, with the only thing standing out about him at all being that his particular method of revenge is quite harsh. I've honestly never understood why some people seem to be so convinced that he should be labelled as pure evil.