Welcome, Rosiegirl!
I can't believe the threatening message you got. I remember the original Rosiegirl's posts on the BASSA forum before I resigned from the union. It is a wee bit amusing that the "person" who messaged you, assumed that you'd want people to think you were the BASSA one, who always seemed to me to have no grip on reality. You clearly do, and it heartened me to read your posts.
Well done you for having the guts to tell us your BASSA story. You really aren't alone. I was with them for decades, and along with others, resigned. I'm currently non-unionised. I felt it was the only way I could send a message to UNITE that the BASSA leadership needs to be dealt with. When it is, I will happily rejoin.
In the meantime, in 23 years with BA, I haven't needed BASSA representation at a disciplinary, as I don't steal from BA, and am not rude to passengers. Judging by the things you've said and the way you express yourself, you won't be up for a disciplinary anytime soon, so don't worry on that score. And if you have an accident at work, there are a ton of solicitors' firms who will fight on a no-win, no fee basis.
We do need representation in negotiations, though. So I'm waiting impatiently for TW to do something about his problem branch.