I'm not sure it would revers the outcome. Recall Browning. PVS is not a necessary prerequisite for natural death by starvation, incapacity (inability to contemporaneously provide competent medical instruction) coupled with a previously expressed wish is enough.
I think Greer didn't want to "push his luck," as a non-PVS but incapacitated Schiavo would expand the class of people that could die naturally by dehydration, from those as Browning that had written wishes, to those as Schiavo where the patient's wishes were determined by testimony of others.
I do think that the expanded class (patient's wishes found by clear and convincing evidence and patient is incapacitated) is inevitable under Florida case law. The only difference is the evidence by which the patient's wishes are divined.
With the amount of publicity the case had gotten, a finding that Terri might not be PVS would have totally put the brakes on the case. Such a finding would render totally unjustifiable Michael's refusal to allow therapy to allow Terri to communicate. Although the Hugh Finn case set the precedent that even a clear and unambiguous desire to be given water can be overridden by a court's declaration that someone is incompetant to make such a decision, I don't think a court would have dare to have accepted that argument in a highly-publicized case.