My mother always said that if she was ever incapacitated and was not aware of her surroundings that she did not want to be hooked to machines simply to keep the body alive. She had seen her father have Alzheimer's and did not wish to go through that herself.
My mother did get Alzheimer's and when she got to the point of not knowing anyone or how to eat we had to decide whether to allow feeding tubes. The one girl in the family wanted the feeding tube. Her argument was that not using it would be allowing her to starve to death. I argued against it because of Mom's wishes and I had done week long fasts before and knew that after 1 or 2 days you do not get hungry. I was alone in my argument and was out voted by siblings.
The next couple of years were truly heartbreaking. Seeing Mom gradually draw up into a fetal position with a gaping open mouth was pure hell to see. I wondered if something was hurting her and she could not tell us. I was actually relieved when she passed on and felt guilty for feeling that way.
I would not wish that decision on even my worst enemy.