Rollback can restore the development database together with the code (that's the checkbox you saw). That's why your test users vanished.
The published app should use its own production database, separate from dev, and a workspace rollback doesn't touch that. But verify it for your project before launch: look in the Database pane whether you see a separate production database, and check which DATABASE_URL the deployment uses.
Whatever the answer: set up your own backup before real users arrive. A nightly pg_dump to somewhere outside Replit costs nothing and you'll sleep better.