So my idea solves for this exact situation

Everything about the group - name, description, mods, members, ban list, rules for posting (really just preferred instructions for client filters), relays, everything - would all be contained in one canonical event. Then that event could be hosted as many places as possible. Then all the other event kinds, posts, comments, upvotes/downvotes, etc would be stored on at least the relays listed in the canonical event.

So in your case you would be able to publicly see when the members list and/or ban list was updated to change your status. (And theoretically you could also have a kind that is moderator endorsements before a canonical kind is considered official, so you could see which mods endorsed this update.)

You wouldn’t lose your identity or any of your previous posts, provided copies of them still exist somewhere, it’s just that default client behavior would now be to filter your content out and prevent you from signing new events from your npub. If you had a copy of your data you could archive it, display it, etc.

It wouldn’t keep the mods from kicking you out, but it would keep them from being able to pretend they didn’t know what happened and have you lose all history of your account like it never existed.