Do note that when I said "truly vegetative" I meant without a soul.
I take it you believe it is improper for a Christian to have a "living will" which precludes the use of a respirator. Of course, none of our artificial means can prevent the sovereign God from taking a soul to heaven. Whether that means (1) we're obligated to keep the body living by any and all means at our disposal and/or (2) God will stop the heart from beating at the moment when He takes the soul, would seem to be open to debate. I certainly don't claim to have the answers.
I am not necessarily opposed to a living will - though I think, without a special document, it is much more likely that a person will be killed against their better judement than "forced to live" against their better judgement. I say better judgement because people may often say "I wouldn't want to live that way" not knowing how little suffering being on a respirator takes place and how often people survive after being put on a respirator. There is vast ignorance in the public about end-of-death situations.
There is also a "will to live" document available. The best approach for most people who don't want to be starved to death is to appoint someone you trust as your legal guardian (of course, this as in the Schiavo case could be fraught with difficulties).