Florida law...and the rest of the 49 states... should.
How can anything less in questions of life or death be acceptable?
There are certain circumstances where written instructions would not be practical, but where the will of a person not to be sustained is made clear beyond any reasonable doubt. There should be some legal procedure to deal with such cases. If judges could be relied upon to exercise reasonable judgement, this issue wouldn't be a problem; as it is, I think legislators need to be a little bit more explicit about what things may be acceptable and what things are not.
Among other things, if someone has left written instructions that they do not wish to be fed by G-tube, but they are verbally requesting otherwise, should the written instructions take precedence? Or should there be some means of accepting oral statements in such a case?