It was never intended to be put to the uses that legislatures and courts have crafted for it.
If it exists at all, it is a syndrome with varying causes and a diverse set of prognoses.
As a diagnostic category, it should probably be abolished, but it's too useful to politicians and judges for that to happen now.
PVS, especially the term ‘vegetable’ should be abolished on moral grounds: It is an inherently dehumanizing term, as offensive as calling a race of people sub-humans or monkeys. Actually worse, as it is calling us to have less concern for humans than we do for domesticated animals.
No human being is a vegetable, and just as losing one’s limbs doesnt term a human into a worm, losing consciousness doesn’t turn a human into a cabbage.