It is not so much just surviving but when cognitive function drops below a certain level there is nothing but a silent shadow of the soul that used to thrive in that body.
Most die a quiet death after weeks of vegetative stasis. It is really the worst of all diseases to get. And no one knows why but it hits white guys between 45 and 60 years the most. Great.
My mom received the stage IV diagnosis when she was 83...she lived for 8 months but only needed full care the last few days...She wanted to go to bingo on a Friday and passed away the following Thursday. I was so thankful to have those 8 months with her in spite of 2 brain surgeries, chemo and radiation.