There's the rub. If you are in a vegetative state, it does not matter, you don't "think". Remaining in that state or dying does not matter.
In a vegetative state there are no preferences. So keeping someone alive waiting for a cure, petrie dish neurons, is okay. It is not a bother to them. If you believe PVS. I don't, it is crappy science.
But go to sleep tonight, and sleep well. I don't think we disagree that much and I am sure your MD husband would not give up on a patient, unless he really thought there was no hope. And it would not be a monetary decision.
All the best.
DK