Diabeties as earlier said to be Royal Disease has not just restricted itself to upper classes but is found to be in middle and some lower classes. Diabeties has been a disease of developing and developed countries. Diabeties as such is not threatening, however, the various problems associated with it makes it serious and threatening e.g, a small cut in the finger may lead to the amputation of finger in some cases, if infected...that is Diabeties.
Diabetics are always at risk of some secondary disease or infections.
Now as far as diet is concerned, it has a big effect on Diabetics. In some hospitals a dietician is solely hired for the purpose of prescribing and maintaining the diet for diabetics. So Diet has a major effect on diabetics. Diet majorly organic and Raw like of vegan has a role in controlling the diabeties. However, it is just an adjuvant for the medical treatment. There can be some cases where only maintaing diet would control the Bld Sugar, however those patients would be having mild or moderate increases in Sugar lvls. But the constant high sugar patients in no way can be treated by merely adjusting the diet. I hope you won't be led away by just stories or events. Remember Every patient is different, and so is the treatment.
I also agree with you regarding the corruption in medical field. The money is truely a b****. However, there are also some corruption free practitioners. Hope you find one and may your father have long life ahead.