I would suggest specifically asking the surgeon (and whoever you go to for a second/third opinion) about your concern with using part of the currently inflamed tendon. Perhaps the doctor expects that removing part of the bone will reduce pressure enough to allow the inflammation to heal. At the very least, knowing more should help with your decision making.

I had surgery 20 years ago to repair a chronically inflamed tendon in my ankle. They removed the damaged segment of tendon and replaced it with a piece of one from my foot, and also moved the heelbone inward about 1/4 inch to relieve pressure on the troubled tendon. It was a long, slow, gradual recovery period, but after about a year I only experienced pain from impact (like jumping) and had no problems walking as long as I wore shoes with good arch support. Part of the rehab was re-learning how to curl my toes, because the foot tendon they used was the one that controlled that motion.

Prior to the surgery, the doctor didn't want to tell me too many details about the process, because I think he felt it would be upsetting for me. I can see how some people would not want to know exactly how he planned to "move my heelbone," for example. But I was more comfortable knowing exactly what he was going to do so I asked lots of questions. It helped to understand the complexity of the procedure, for making decisions beforehand as well and setting expectations for the recovery process.

Good luck.