From what I remember reading, anterior open bites relapse most often for whatever reason (maybe tongue thrusting). Work on tongue position and correct swallowing now ahead of time. Impaction itself doesn't relapse (i.e. your jaw won't grow down and become gummy again) but the open bite might. Regarding the lower jaw, auto-rotation is basically CCW movement from the anterior impaction and should be pretty stable since the condyle will likely just be rotating in the fossa instead of being re-positioned. I guess it can move as part of an open bite relapsing or muscular pulling. That's my understanding of it. You should ask your doctor, though, to put your mind at ease and know what to expect.
I don't have any examples of over-impaction, but I agree it's a legitimate concern since it ages the face so badly. I've heard of people missing their gummy smiles after so prepare for that mentally. Good luck, man. It's been forever.
