Guido's gill curl never reversed. However, I have continued supplementing his calcium not with pills, but with shrimp shells... When we have shrimp for dinner, he gets the shells and tails along what ever else is on the menu! However, his isn't that bad (I have seen photos of RTCs where you could see the red of the whole gill). Also, I love him, no matter what. It's too bad it happened, but he seems happy.
The vet's advice may be more useful if one catches it early, or as a preventative measure, though. I'm not discounting it at all, but it must have been too late for Guido.