I am pretty sure that the patient has to agree to have his leg amputated. If he does not give consent you can’t just wheel him into the OR and amputate.
People have the right to refuse treatment. If he didn’t want amputation they would have to try antibiotics and wound dressings. They can just wheel him into the OR and amputate.
just like a Jehovah Witness person can refuse a blood transfusion even if it means death.
good or bad, people still have control over their bodies.