That would be my idea of hell, to have my body kept going by machines. To my mind, the spirit, mind, soul... call it what you will, has already left by the time a person reaches a vegetable state. What made your loved one the person they are, no longer exists. It has already vanished, either to Heaven, to the spirit realm, to the air or whatever your beliefs are, and there is nothing whatsoever on earth that can ever bring it back. Therefore, keeping the shell going with machines is just prolonging the agony; best to switch the machines off, let the person die and be at peace, and finally allow yourself to grieve for them.