I have had rather extensive experience observing this and also had a NDI when I was 21 and in the ICU for many weeks due to swine flu. A person who is ready to die is often in an altered physiological state that bears little resemblance to the usual. This is not about rational decision making but about messages coming from deep within the body and psyche. A person who is dying and a person who is not are often speaking different languages. I know it is heart breaking, though, and feel for you.