If my husband told me to pull the plug on him if he became a vegetable, I wouldn't be able to do it immediately. There are cases where the person regains consciousness, inexplicably.
But after 8 years (geez, perhaps sooner? I don't know), I'd follow his wishes, because I'd be sure he couldn't wake up.
Ugh, why am I following this horrible story anyway? Now I've got to figure out how to make a living will or Dubya will decide my fate.