I work at a big branch pet shop. I know if you return a sick creature, we send it to the vet (we are lucky enough to have a herp/amphib vet by us.) We go by what he recommends, if treatment is in order than we treat it, if euthanasia is the recommended course then we do that. So I can't say he wouldn't be put down but it's possible.

You can get pimafix from most pet stores, it is a fish medication that works with amphibs. It will be .5 ml per gallon when dosing. Also might try upping his diet a bit. What are you feeding?