He didn't make it
Sorry you lost the little guy. It's been my experience with cories that while they'll grow back the thinner membranes of their fins if they get torn up, once the "spine" of the fin is gone, it's gone. Worth trying to save 'em though. I've a ragged little guy in my main tank that's the sole survivor of a pretty horrific case of fin-rot. He lost about 60% of his tail and dorsal fin, all of his belly fins and his lovely yellow side fins are tiny yellow stumps. Almost euthanized him the first year when I realized he wasn't going to grow back any more fin--but changed my mind when he out swam my nets four times in a row!
It's been a little over six years now and he's still going strong.
The pickle jar was a good idea, as was adding the substrate to carry over beneficial bacteria. When you've got the funds, you might want to pick up a small tank (2.5g or one of the "critter keepers") and keep it packed and ready to go as a QT or isolation tank. Easy to just put all the supplies in the empty container so it's stored together and ready to go at a moments need. Mine has a small heater, air pump and stone, nano sized HOB filter that readily takes a cut down pad from one of my tanks, a cut down piece of black PVC piping for cover along with a couple smooth rocks to hold it in place on the bare bottom and a bag of aquarium salt.