Never sign a Living Will.
I've got one, but it is very specific as to who can make any decisions and under what circumstances.
Never sign a Living Will.
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No, you should have something in writing. Some believe in a "Will to Live" which would indicate that the signator wants to be kept alive no matter what. If that's your choice, then do it. But have something in writing.
This is not the same as the Schiavo case. In that case, there was no living will or anything in writing. Here, we have a signed document, but presumably one that goes into effect when a person is incapacitated to the point where he/she cannot make these decisions. Seems to me this gentleman is still lucid enough to make his own decisions; so whatever his wife wants, including trying to enforce the living will, should not apply.