Mine very resolutely (and he usually sticks to his word) said good bye, I will never contact you again - and two weeks later sent an email. I didn't respond, and another two weeks later sent another brief email. Both were deeply apologetic, both said he missed me. (The most recent email sparked us initiating minimal contact again, which has been okay - no rages, no drama, no attempts to get back together.)
Just a word of caution here: it could be a form of manipulation, a way back "in" so to speak.
I was NC for 3 years with my pwBPD. We started minimal contact and she seemed well regulated. That turned into a relationship that lasted a year (closing now). Various things have came to light recently for me that had shown me that I shouldn't have bought into the image she presented me.
You know your pwBPD better than anyone here, just be optimistically cautious. That's all I'm saying
