What is the rate and likelihood of cerebral atrophy in vegetative state after brainstem stroke?

High: Cerebral atrophy occurs as the result of brain damage. Therefore by defitioning, death of brain cells may occur as a result of injury to the brain including: stroke and traumatic brain injury. Other causes of atrophy are specific diseases and infection or inflammation of the brain. Risk factors include advanced age, brain injury fh of alzheimer’s disease, huntington’s disease, or siminlar disea.

That's irrelevant: You're making a common layperson's mistake: You're confusing a correlative marker with the thing itself. The presence of cerebral atrophy either during life in imaging or pathologically after death tells you nothing by itself. What matters is how well a brain WORKS, not how it looks. It doesn't really matter how the brain of someone in PVS looks. What matters is the PVS. A fate worse than death.