Dear madam/sir i can understand your concern i am very sorry for condition of your dad in my opinion the toe might have been in the state of gangrene or excessive bone infection. Gangrene is a condition in which the blood supply for that organ is blocked and making it to turn black colour.There will not be any viable tissue in that organ. the best treatment for gangrene will be removal of the non viable tissue. But toe amputation is considered only when the bone is infected. In this kind of scenario there might be uncontrolled blood sugar due to infection in the body.starting insulin and continuing it until wound heals is the best option. The blood supply of the foot can be investigated and in case of any block corrective surgeries like popliteal bypass can be done to avoid amputation.prognosis depends on level of block and type of block. i suggest you to check the blood supply by Arterio Venous doppler study. insulin will reduce the recovery time and helps fast healing of wound along with good control of diabetes. regards Dr vamsi Diabetologist