What could have happened is the fin rot, if it was bad, could turn into dropsy because the bacteria just moves from the fins to another part of the fish's body. this happened to one of my bettas a few months ago after our power was out for 4 days. Fin rot, that didn't respond to antibiotics and then about a week later, dropsy.
Betta revive, in my experience, has not been the best thing for fin rot, but a lot of stores only carry betta revive so they recommend it for pretty much everything. I've never had success with it for fin rot but it worked for a mild case of ich years ago. Although I don't think it's designed for that..
Best luck with your fish :)