My Grandfather Is 96, About To Be 97 Next Month.

My Grandfather is 96, about to be 97 next month. He had a blood infection a few months back, but they said it was gone. He is diabetic, and has had sores on his right toe for a few months not, but have been under close watch. He is still walking, but the infection has gotten worse. He has gangrene on his entire big toe. Doctors want to amputate just below his knee, but now are saying there is no point. The doctors said it is about to fall off. He has lived a very long, and fulfilling life, but that doesnt make it any easier. I am preparing myself to let go of him, and am just trying to see if I should prepare myself to have him around for months (2-6 Months) or if it is going to take over faster than that. Also I am wondering what other sort of side effects are going to come along with it since the doctors are just trying to keep the staff-infection under control. Does this kind of thing start effecting their mind? Will he be uncomfortable?