I checked my database size via terminal command: du -h /var/discourse/shared/standalone/postgres_data
My database was down to 83MB from 7GB previously. So it seems to have really been overwritten by the update. I ran ./launcher cleanup as part of the PostgreSQL update (as per the update directions), so there’s nothing to go back to except my backups. Discord wasn’t just disconnected from the database somehow.
I restored my backups, I can live with losing a couple of days of posts (my own fault for not backing up before updating). I just wish I knew why the PostgreSQL update overwrote my database, since I’m going to have try do it again eventually.