One would think that a revoked advance directive should
be disregarded. Why isn't it? Here's one approach, on
a Moral Absolutes basis. This is a mere sketch. We have
no rights in ourselves, and once one grants as a premise
that *sometimes* one has the right to refuse medical treatment
("ordinary" i.e. efficacious, routine, non-experimental)
treatment, one leaves oneself open to death by neglect.
I concede most ppl do not realize they are doing this. Also
that the opposition to the Culture of Death includes many
who don't accept this analysis. Wish I could put it better.
"The law" says that the patient always has this right and power. Once man takes that power, which is contrary to God's commandment, no good will come of the decision.