Sorry to hear your update. My husband was offered the same options, but decided to go with a below the knee amputation. The pain he was experiencing and the lack of certainity the other treatment methods would be successful led to his decision.
The amputation was hard on him mentally and physically. He got thru it. He probably would have fared better if he didn't need both knees replaced so he could walk with his prosthetic leg. But he has opted against knee replacement surgeries because of the serious infections he suffered in dealing with the ankle. So he is in a wheelchair, but actually does very well. He gets around as well as if he was walking.
If you did the amputation and got the prosthetic leg you would be in pretty good shape. Know it's an awful decision to face, but it's do-able.
Best of luck! Keep us posted!