I can relate worrying about it. Exw did the same, ‘just’ blowing up the r/s as I didn’t had time to go out for a walk with her, or as exw wasn’t personally invited (yet) by her sister for her birthday. It kind of scares you of what will be next.
It was exw’s ultimate threat, as exw couldn’t come up with anything else anymore. That pattern lasted several years and before I knew anything about BPD (later knowing about BPD, I knew and despite all, that the r/s would end one day).
But my response scared her as I said ‘You want to stop? Then you will be the one that leave, never me!’
Well, in her ultimate outburst exw indeed left just with only few boxes, as she did when she was 18yrs. old dumping her parents in exactly the same way.
I really understand your position and think it is very wise to take precautions as divorcing a BPD will be a high conflicted one.
Remember, feelings ARE facts for pwBPD(!), so you are the one that will need to prove facts!
So yes, you need to document, file important documents (in a safe deposit box at the bank), scan and back up your computer files. Don’t forget passwords…
And yes, document (with dates) threats, outbursts, etc. I did so for many yrs. and even handed some over to the family doctor! It became very handy during and after that divorce of exw.
Reading your intro, 20 yrs. through the drain will be very, very hard!
Despite it is not you, it is her, her actions affects you, your family, your finances and your future!
Be strong, read, learn and apply as much as you can.
Most of all, be kind to yourself, build a support network, as I did by informing some family members and close friends, it helps!).
For you and the sake of your family, I really hope ‘that’ day will never come!