Earlier quoted context omitted.
Sometimes when communities die or are killed, they don't come back. Nobody knows where to go to re-convene.
This is different because mastodon.technology will keep operating until December 1st. This leaves them plenty of time to organize a move by discussing it on the platform like they always have. They might move to different Mastodon instances (via the built-in migration system) or find a new network, but they are not getting killed with no way to find each other afterwards.
At the same time, based on my own personal experience, it is absolutely impossible to get people to move to another platform or service even for the purpose of discussing future plans.
My exceedingly strong advice is to have multiple points of presence defined as a matter of course, one of which should be a simple email list (which provides persistent contact information), regardless of any awareness of an impending platform shutdown.