Bottom line unless your DOA don't expect that living will to mean jack **** once they put you on machines.
At least ideally, this is patently false: there are legal statues in most states that recognize the authority of advanced health care directives, and any hospital which did not respect them would open themselves up to all sorts of legal hell.
The point that seems to be getting lost in this discussion is that the woman did not have any sort of formal DNR order on record at the time of the incident. (Granted, even if she had, the provision in the state law would have mandated this course of action anyway, but bear with me for a moment.) More to the point, even if she had discussed an aversion to prolonged life support with her husband in the past, there are no guarantees that she would feel the same way in the case of being pregnant. I feel pretty sure there are many women out there ordinarily opposed to extraordinary life-sustaining measures who would be very willing to be subjected to them if it meant allowing her child to make it. I think the intent of the provision, as clumsily as it may have been executed, was to make that provision clear to women up-front if they were to create a formal advance directive.
Regardless, if the medical details about the case are accurate, it unfortunately sounds as though the fetus is almost certainly brain-dead, and that at this point prolonging life support is little more than an extended cruelty to the family. Their best bet now may be to just hold tight until the fetus is able to be properly tested for brain functions, and then hope for a court order to remove support if the tests come back negative.