I'm so sorry about your cat :sad:.
Have you considered consulting a homeopathic veterinarian (not just a homeopath make sure it is also a vet)? I have recently become quite fascinated with that area and have been taking my older dog and have seen some good results and have know others with good experiences. I think at this stage it would definately be worth trying before you consider amputation.
"Never doubt that a small, group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has." - Margaret Mead