We have published this at moodle.org see https://moodle.org/plugins/view.php?plugin=block_eledia_usercleanup.

This plugin deletes inactive user accounts. The cleanup process runs with the Moodle cron.

The cleanup-process runs in two steps for each user. If an inactive user is found he gets a notification mail and is marked as notified within this plugin. When the user still has not accessed the system after a choosen timespan he will be deleted in the second step.

The process checks the last access time stamp of the user against the present time stamp.

When a notified user loggs in again before the deletion process starts, his notify entry is removed with the next run of the cleanup process.

You can configure how often the process is started by a time interval in days.