Interestingly, from this article one can conclude that, per federal law, one cannot pull a feeding tube unless clear and convincing evidence is available that the affected person would wish it to be pulled under the circumstances. I don't think most people would agree that Terri's husband's interested hearsay testimony constitutes clear and convincing evidence. I know that per legal technicalities his testimony is not regarded as hearsay, but give me a break: society has watered down the marriage contract to such an extent that no one can seriously regard his testimony as anything but virtual hearsay.
Clear and convincing evidence can be a co-worker or two from about ten years ago, as happened when they wanted to kill Nancy Cruzan.