I've left too, and did wonder about re-joining to vote, but it's pricey and I've never had any benefit from membership (I've been lucky enough not to have contract irregularities or need any help my agent couldn't provide.) I didn't want to pay over £100 to an organisation in which I think the rot is set too deep to salvage.
I suspect Joanne Harris will win and she and the vocal Publishing Puritans will gloat on Twitter about defeating the evil transphobes and how good always triumphs etc etc. Meanwhile, in the real world Mermaids are crumbling, Maya and Allison were vindicated in court, the Cass report is shining a spotlight into safeguarding black holes, Stonewall are being exposed as a clownshow and the vast majority of authors I know well enough to be honest with are well aware that these are seventeenth century values repackaged for the social media age.
If Twitter is the public square, it's currently in the era of occupation and everyone knows you can't speak freely there. But those conversations are still happening in real life, and Joanne Harris and her ilk are foolish if they mistake lack of public challenge with agreement. She might win this election, but she'll be left at the helm of a discredited organisation with a declining membership, crowing about it on a platform that people are abandoning in droves.