What are the last stages of diabetes? I have a good friend with Type 2 diabetes along with an IV drug?

addiction for most of his life. His feet are black & blue and very painful to the touch. He can barely walk. He was diagnosed about 10 years ago. He has suffered temporary blindness for a few days but his eyesight returned. He has ignored a proper diet and he eats what he wants to. His entire body, especially the stomach area hurts to touch. Because of his IV drug use he has extremely poor circulation along with no veins. Does anyone know what the effects IV methamphetmine drug use and diabetes has? Both diseases are serious, but what is the worst scenerio besides death. It seems like his body is rejecting everything. Any help or advice is sincerely appreciated.