Renal failure and on a respirator? Doesn't sound like he has much quality left in life. The document may have been signed when he was well, but it serves him now in this instance.
I took care of a lady in her 70's who had been on dialysis for years. She was still really sick and finally decided to stop the dialysis.
It was strange watching her die, but it was her choice and I am all for the right to make end of life choices.