There is my one: discourse-auto-suspend. As the name suggests, it suspends the user after a period of inactivity.
The official one Jeff is talking about is Discourse-auto-deactivate which deactivates users after a period of inactivity: GitHub - discourse/discourse-auto-deactivate: This plugin will automatically deactivate stale users so that they need to recomfirm their email in order to login in again · GitHub
Deactivated users can log back in simply by confirming their email address, so I think you want discourse-auto-suspend