If they are not going to provide for the protection of the right of a person to life....none of the rest matters.
I would also point out that very shortly before Terri's mysterious "collapse," she had stated before witnesses that she wanted to divorce him, i.e., she DID NOT WANT him making important decisions for her.
Your post is a perfect example of why an examination of the Constitution is so important. Education. The clause you highlighted has nothing whatsoever to do with individuals, but with the states.