Re-purposing a Discourse installation for a yearly event

On a SSO-enabled site, if I log out a user, prevent him from signing in again via SSO, and deactivate his account, is there any way for him to interact with Discourse anymore? He should not be ably to reply by mail, should not get any new mails and be unable to re-validate his address because he cannot login, right?

I am trying to kick out users that took a course last year, while ensuring that they can login again if they sign up for a new course (which grants them SSO login once again).