At least for the foreseeable future, there will be uncertainty over whether some PVS patients are in a cognitive state more like locked-in syndrome. (National Post)
Consequently, it might be prudent for individuals to address this situation in their advance directives. For example: "I do/do not want to be sustained with life support if I am diagnosed in a PVS, even if fMRI shows I have some responsiveness." Of course, if the fMRI data shows that the patient has decision making capacity, then the patient could revoke the advance directive.