No. once you have diabetes, it is for life. There is no cure other than a pancreas transplant. It does not go away, but it can be controlled well. Your grandfather can bring his blood sugar readings down by watching his diet,..limiting the amount of carbs he eats, stays away from sugars, things made with white flour, like breads, cakes, pastas, and white potatoes. If he counts carbs, he can eat things things in limited amounts. He needs to take his meds as prescribed by the doctor, and if they seem not to be working, he needs to see his doctor, his meds may need adjusting or changed. Tell him to get some daily exercise, like walking. Signing up for some diabetic ed. classes is also a good idea. He will learn a lot. As to the 2 answers above about type 2 being reversed or "resolving" itself with diet and exercise....false.
You can only control it, it is never resolved or reversed.