First off, unless this happens within the next 15 days, the point will be moot with regard to the current law.
If Jeb had the authority to intervene, I would expect him to defer to the courts unless he had extremely strong reason to believe that they were in error. In Terri's case, evidence exists of numerous conflicts of interest which Greer refused to acknowledged; Greer's refusal to acknowledge such conflicts of interest suggests he likely has some of his own.
Basically, I would interpret Jeb's power in this case as being a civil-law equivalent to the pardon power. Just as criminal-law cases are too important to be left entirely in the hands of a single trial-court judge, so too should be certain life-and-death civil law cases.
Do you have a problem with such law?