Three legged dogs for hunting!?!

Let me just throw something out there to you. You said he still has feeling in his foot and leg which is a good sign. He MAY have lost mobility and muscle mast because of a condition caused atrophy. It happens from different things but one of the things that causes
atrophy is lack of use of a limb and muscles associated with that limb. If this is the case you will have to physically move the leg back and forth and get his range of motion back first. Then start exercising him and he will build back muscle. All this will take a lot of time and effort on your part. Let me give you an example of my experience with atrophy. I fell off a roof and totally separated my shoulder. I Went through surgery and they put me in a sling block with no movement what so ever of my arm for 6 weeks. When they removed the sling block my arm was locked and no way to move it. By not using the arm and muscle for 6 weeks it caused it to lock solid. This is called
atrophy. My muscles in that arm really shrank. It took a few months of physical therapy with him pulling and stretching to get my arm to loosen up and get my range of motion back. After that I worked on building back the muscle.
Maybe this is the case with your dog. Maybe not. But I wouldn't rush to amputate his leg. Bring him back to the vet and let him decide what course of action to take. Sorry for the long winded reply but I thought it might be helpful. Keep us posted.