Euthanize or continue treating?

It sounds like it's suffering to me. I doubt that it will recover completely and even if it does, are you going to put it back into that tank with the other fish again? If not it will have to live in isolation forever. If it's getting a bend to the body, it sounds like it has more serious damage than just the fins. I would euthanize it. A fish doesn't usually come back from such extreme damage. Sorry. I hate it every time I have to euthanize a fish, too but sometimes its the best alternative.