Have you ever seen someone who is physically and mentally abusive (possibly a narcissist or a person with BPD) change, especially if they've been this way to every partner they've had for years?
I can't speak personally really, but from my research, no. A VERY hard MAYBE with BPD, if they WANT to change and after MANY years of DBT Therapy, they COULD change but it most likely won't happen. Narcissists will never change. They don't think anything is wrong with them, they're getting all of their needs met no matter if it hurts anyone or not. They will deny being a narcissist and never seek treatment.