I'm not trying to spell out every detail of what the law ought to be -- just making the point that the law needs to spell out enough detail to handle the difficult cases without leaving everyone wondering if decisions were made unjustly or with slimy ulterior motives. The law should be prepared to handle a situation in which, for example two parents disagree on what to do with a severely brain-damaged infant. The law might spell out a procedure for appointing a completely disinterested guardian to make a binding decision, or it might spell out that if either parent wanted the child kept alive then it must be kept alive. It's the lack of ANY clear procedures that enable a single judge or a default guardian with a conflict of interest to inappropriately steer the legal decision-making process.
It is my own opinion that the door to death by starvation/dehydration should have never been opened. It is cruel and barbaric, but since it has, this seems to me to be a rational guideline:
If a person is not wanting food BECAUSE they are dying, then don't force feed them, but don't take away food and water when they're not dying because somebody else thinks they should be. It really seems pretty simple.