Hello, I m afraid an advanced diabetes with impaired renal function (which indicates that important damage has already occurred throughout his body) is destructive for blood vessels that provide the blood supply to the extremities particularly the feet. This is why diabetics should be very careful to avoid even the slightest wound on their feet. When gangrene has occurred it would be very difficult to avoid amputation. Trying to avoid an early amputation might mean that a bigger part of the foot might be cut later. Revascularization can be done on large vessels. The problem with diabetes is that besides the large vessels, the small vessels also are affected. Of course I couldn t talk about the specific case of your father, without knowing the results of radiological testing but I ve described you the basics. I hope your father s situation is more clear now. If you need further explanations, please ask and I ll be glad to provide them. Kind Regards!