the way I think about this is that when one has unsolved problems and anxiety or stress then the original symptoms of PTSD are liable to intensify. If I were you I would look at your life and try to identify your sources of stress and be more active in doing something about them as a way to prevent any suffering with PTSD symptoms. You are in therapyfor a long time and perhaps you have to refocus your efforts on the source of current stress.
Who knows? Nobody collects reliable statistics on such things. There are a few double blind studies on different kinds of therapy and on medication, but not a lot. And people don't react the same. Some get better, some don't, but I'm not sure anyone knows exactly why. Some feel that people who have underlying depression have a harder time getting over anxiety disorders, so that's an avenue for research. Good luck to you.