My sister in law has BPD. She's put my inlaws through hell. Dropping them from her life just as their son, my husband, died. She's even rejected her own child. She's been so cruel to them so I can relate a little.
You are going through the hell of raw grief. Just breathe and do the best you can. A cliche I know but take one day or one hour at a time. That feeling that they've just suddenly vanished off the face of the earth is hard! Hang in there. We're here if you want to vent more.