I don't handle this for a school district, but for our company.
When a user leaves email delegation is set up for the manager. At the same time we add a date field to one of the Google custom fields. This is the departed date. We also move them to a departed OU. Every month we run a report of users in the departed OU, and grab the email, departed date, and suspended status. We remove anyone who is currently suspended (They are already done), then we get the departed date for any active accounts. We sort, and for anyone whose departure date is over three months ago, we remove delegation, and suspend the account.