Actually no, it won't.
It's possible to determine that significant damage occurred prior to dehydration, but it's not possible to tell how much functionality remained. Further, no type of mere structural examination (whether CT scan, MRI, or autopsy) can reliably ascertain a patient's clinical condition. There are people who can walk and talk whose CT scans would suggest that they couldn't possibly be alive (and yet they are).
Brains are very weird and interesting things. Although there generally seem to be limits to an adult brain's ability to route around problems, for many perceived limits there are cases that exceed them.
I agree that there are exceptions to almost every rule, but the permanence of her condition is unquestionable. As to "functionality" as you say, I think 15 years' clinical experience with Terri, together with the autopsy report and the clinical judgement of most experts,... overwhelming for those who can see it. I can't say that I'd do everything that MS did, but personally I'd feel much worse keeping her "alive" artificially in her condition than allowing her to pass. I'm sorry to say again that the dehydration argument doesn't wash, nor does it change meaningfully anything I have said.