I am avoiding friends and focussing on work and then "preparing" myself for drama.
Can you tell us more about how you "prepare" yourself for drama? Which drama? What are you expecting?
woven this delusion that my dad has been plotting against her for the last 5 years, tapped her phone, recorded her, had an affair with a family friend he is running away with, gaslighted her and is going to shame her in court and she will be left with no one and no money.
Yep, this is sounding familiar in a few ways. It was a bit different with my mom: her bf was going on a road trip back to his hometown and visiting people from his past including a woman. Mom wove her own delusion that he was "courting" another woman and even gave this woman a ring. My mom was emotionally destroyed - like a 14 year old girl that's just been heartbroken and going to die. We were naive and stupid enough to take her at her word (roughly 12 years ago). We had a conversation with the poor bf who was horrified at what we were suggesting - mom being the only source of the info - and he got mad at us for insinuating things which weren't true. He was right. Then because he was mad, mom blamed us for making trouble for her, when what we were really doing was trying to support and defend her from a man she told us was not being faithful. What had happened, was that in her mind, she had imagined the worst thing, which was her bf leaving her for another woman (BPD and fear of abandonment right? But we hadn't heard of BPD back then, and were clueless as to any possible mental illness). Because bf was on a trip and visiting old friends (including women), these "imaginings" all became a FACT for her. But it was a delusion, and completely untrue. My advice is let your mom have her delusions, and sort them out herself, otherwise the drama for you will escalate, and never end. That was the last time I trusted
anything she said. Too often, the info is distorted, and because the pwBPD believes it to be true, it's hard to tell when they're lying. My observation is it's better to let them figure it out themselves with natural consequences. By not getting involved, you can't be directly blamed. You'll still get blamed for other things as you know, but at least you won't get blamed for that!

She refuses any contact with my dad who is heartbroken. He is a good man, that is not perfect and has his issues, but is being accused of awful things that are not true.
I go to counselling with my H because of my mom. It is super helpful for both of us, but especially me. Is this something that perhaps you and your dad could do together? What do you think?
Last year on the anniversary of my grandfathers death she seemed to get worse.
Yep. Family deaths are hard on a pwBPD, as it seems to trigger the feeling of "abandonment".
At the end of my grandfathers illness (the last year of his life), she was horrible to him. It seemed like she resented him - she remembers it all very differently.
This doesn't surprise me. My mom was the same during my dad's terminal illness (dementia). She couldn't cope with the stress and was SOO emotionally abusive to the poor man. It was cruel. We reported it to his case manager, who worked harder to get him into long term care faster (and away from my mom). Now when she thinks back, she was the perfect loving wife and nurse (she was an RN) to him. It's hard for me to keep my mouth shut when she talks like that, but I do. Reminding a BPD how cruel they are doesn't help them or us.
"Maybe we can spend more time together over the coming couple of weeks before you go away. I’ll miss you being away for a month. Love you xxx"
Maybe you just "missed" seeing this text. Or maybe you've been too busy to reply. I've learned that it's ok to not reply to every text, and sometimes no reply is the best reply!