l'm curious if anyone has ever had one try to come back after A break up going so terribly
Hello and welcome. Kells has already given you some great advice so I'll just focus on your question.
With BPD, the instability usually goes in cycles since everything is tied to emotions in the moment. Once a discard happens, the person w/ BPD usually pursues greener pastures elsewhere...in a new friend, pursuit, or romantic interest...and they feel wonderful since everything initially works. But when that goes badly (because of BPD/instability), more often than not they try to reconnect in past broken relationships.
There are a few members here that have been through this type of breakup many, many times. Others have gone through it once and decide that they won't create an opportunity for it to happen again. It really is different in each scenario and your patience will play a big part as well.
Like you said, this is still very fresh and right now you need time to heal more than anything. Take that time and you'll eventually get to where you can see the relationship objectively and make the best possible decisions for your life. Maybe it's worth rekindling, maybe not. I wish you luck either way though!