I found this interesting article on Slate about the case of Terri Schiavo.
I don't see what harm there is in letting her live if it is only a feeding tube. I was under the impression she was on massive life support. If she is really vegetative, then she won't care. I guess the worst case is that she is aware and feeling trapped, but as the article said, surely after 15 years, she's probably become accustomed to it and might not want to end her life. She isn't suffering, so as long as someone is willing to pay for it, why not let her live?
I think a more interesting question would be, if her husband was tired of paying for medical treatment and decided that the tube should be removed, would the case be treated the same way?