Hello and welcome to the forum I think you should definitely consider DBT or another type of therapy because there is no reason to think you cease to exist without your diagnosis.
I don't think much as changed for me before or after diagnosis, though having a bachelors in psych I've known for over four years without a actual diagnosis. I think now I am more aware of my emotions and am better able to control them because I realize they are a symptom.
I am not defined by my BPD, but it is important to understanding who I am.