Depends if I knew/thought there was a chance or not. 

Iv seen to many go through (ok not bike related) end stage CF and my wife at the end stage of cancer and it was horrible. I hated seeing what was happening to my wife and I know she was in so much pain and although I know she wanted to live to so much as I did want her too, I also know she didn't want to be in pain.

I know that if I was at that stage I would just want to die. I also hope by dying and no longer being in pain my family although maybe upset would also know im not in pain anymore and hopefully I would rejoin my wife.

If I was in a state that there was no hope of regaining control of my body and having to rely on others for the rest of my life, again turn me off.

But I guess until your there you just won't know