That is why I stress the importance of either having it in writing, telling other family members or her doctor. I mean, how hard is it to just tell someone else so you have a witness just in case?
Let me repeat, MS broke his vows by committing adultery while Terri was still alive, which renders your argument based on those vows void of any rational logic.
And that is why I stress the sanctity of the marriage covenant. It shouldn't require additional legal arragements.