Not by default. Manifyst ships with Delete All Data on Uninstall switched off, so deactivating or even deleting the plugin leaves your events, slots, signups, and history in the database. Reinstall it and everything is there.
If you do want a clean removal — you are decommissioning the site, or a data-retention policy requires it — turn the setting on before you delete the plugin, at Manifyst → Settings → General. It only takes effect during uninstall, so it has no effect on a running site.
That order matters. Deleting the plugin with the setting off, then reinstalling and turning it on, does nothing to the data left from before; you would have to delete the plugin a second time.
Uninstalling always clears Manifyst's scheduled jobs and cached values regardless of the setting. Only the event data itself is protected by it.
Take a database backup before any uninstall you intend to be permanent. There is no undo.
