Will Falconer, DVM Moderator
That's when quality of life becomes the most important to assess, in my mind L. If there's suffering and a terminal condition, it's hard to deny euthanasia as a kind offering.
I'm not sure I'd know what "fighting to live" would look like, but I think I can identify suffering. It's often most clear to me when the animal is unable to rest and relax. Vocalizing added to that makes it even more obvious.
Ultimately, I think we need to make a "team" decision: owner, vet, and animal in the middle. Each one has something important to say.