Is having a dished-in profile due to premolar extractions reversible or diminishable? (photo)

I would recommend you consult a different orthodontist.  You may have to consult several to find one who would want to retreat a case just finished.  Your arches most likely could be expanded to give you back the facial support you are now missing.  Spaces will be created somewhere during the process since you had teeth extracted but they can be closed restoratively depending on where they are and how large they are.  Have you discussed your dis pleasure with your current orthodontist and showed him the changes you see on the photographs?