Automation of Learner Seats

Is there any way to manage seats not being used?  Other than hoping a department manager calls me to delete an unused Learner ID, I can't figure out how to manage this.  We have 5000 seats and multiple departments across the country. As the Admin how can I make sure seats are not being wasted on people that quit??

I asked the managers to add this to the new employee checklist for hires and the exit interview sheet for terminations but its not working.  Is there anything else I can do??  Run a report of inactive user ID's and hope they quit before I terminate the account?  Seems very manual.  We have lots of turn over in remote locations.