That was exactly what the Terri Schiavo case was about, and why so many wanted her to die before her time.
One of the horrible things about Terri's case was that her family wanted to take over her guardianship and care, but dear Mikey and the court system wouldn't let them. So her Mom, Dad and brother had to stand by while the state dehydrated her to death over a two week period. It makes me furious every time I think about it.