Well i am sure that each case is individual, but in general chemical imbalances do not correct on their own and if there is no epiphany, i dont see how a chemically proven mental illness can improve. It can be ignored, and life situations can mask it, but it's not just going to get better on it's own.
Personality disorders are basically just a series of "bad" personality traits, and your personality gets fixed in your early 20s and it is very very hard to change that.
PD's are more about the way that you are wired, and while symptoms like depression and anxiety can be treated with medicine, the PD can only be treated with therapy and basically changing your outlooks on things.
Often, taking medicine totally takes the problem away for chemically-proven mental illnesses, medication often does nothing for PDs.