I've looked around but haven't found updates on if or where the subreddit migrated.

I searched for instances on Lemmy. There are 4 but they're unmoderated or appear to be moderated by a bot.

The askhistorians.org website still links to the subreddit.

The subreddit itself seems to be open, but the list of moderators is hidden (probably because I deleted my reddit account).

I found some chatter on Discord, but not an actual server.

Thanks!