From my experience as a rescue-worker, I have instructed my SO to never have me on a machine for life support longer than one week before I'm in my sixties, and no longer than 3 days if I'm over.

This is my decision, and I won't go into details, because they are personal and I am not a doctor. Perhaps the point I desire most others get from my post is this:

We are all going to die. Usually unpleasantly. Most often, unexpectedly, even with a prolonged illness.

Plan your death. Plan your medical treatments. There are things you can control, you need to know & state what they are, and have it in writing.