Diet Doctor has great success stories on reversing type 2 diabetes. The most amazing success story I've read is titled: "Type 2 diabetes reversed after 26 years of insulin dependence!" You can read more but googling the article. Here is an excerpt...
"I began your program confused thinking I MUST eat all this food and three meals a day and honestly could not do it! Simply could not ingest that much in one day… did not want to! After a month more reading and viewing every offering on your site I began to understand… there is no rule save be smart and cut, cut, cut carbs. Next I joined up and cut down, exactly like Bernard to one meal a day with frequent three day fast and a miracle has happened!
Diabetes – after 26 years of insulin dependence – is gone. The neuropathy in my feet vastly improved. Crohn’s disease, after 45 years of agony, is in complete remission, cardiac issues are resolving themselves. BP is back to a healthy normal, esophageal issues are hugely improved."
So sorry to hear about your dad. Is he under a doctors regular care for his diabetes? How is his diet? Is he on medications and is he tracking carbs?
Has he been taking insulin and balanced diet? Now his age?
Diabetes complications can be pretty terrible. The best way to handle diabetes is with diet (cutting carbs really helps because carbs raise blood sugars, reducing carbs then helps), and medications. In long standing diabetes insulin is typically used. However, it has to be used carefully and with knowledge to minimize highs and lows.
Some diabetes complications can be reversed or stabilized with normalization of blood sugars. We do not know if this is the case for your father. Certainly he will need to work closely with his doctors for management of his condition.