I'm sorry that this happened to you. What i am about to propose is not a solution for you for now unfortunately. But maybe something to help for the future...Have you considered starting a new presence for yourself and your community on the fediverse (e.g. mastodon, pleroma, diaspora, friendica, etc.)?? This will take work and time of course and maybe not all members will follow you over, but if you start a new commu…
I think you have too high hopes for the possibility to get non tech-geek users to try the Fediverse. If Heavy Metal Community A on Facebook disappears overnight, I think the users will simply join Heavy Metal Community B (on Facebook).
And, separately, while the fediverse is vastly dwarfed in participation numbers by convenional social media...at last count there are several millions of users engaged within the fediverse...Now, that number fluctuate wildly depending on sources from single digit millions of users to double digit millions of users, etc...But there are still quite a large number of people nowadays on the fediverse. I happen to know many users (that i ineract with constantly) on the fediverse who are most definitely not tech-geeks. I win nothing if this community leader listens to me or not...again, i was just proposing a suggestion.