That's not very "persistent" then, is it?
Some patients may regain a degree of awareness after persistent vegetative state. Others may remain in a vegetative state for years or even decades. The most common cause of death for a person in a vegetative state is infection such as pneumonia.
"The adjective "persistent" refers only to a condition of past and continuing disability with an uncertain future"
"A wakeful unconscious state that lasts longer than a few weeks is referred to as a persistent vegetative state."
An excellent summary on PVS. Cuts both ways on the Terri issues.