by Jaswinder Singh.
Hi Nathan,
Are you talking similar to longtimenosee feature.
In site admin >> plugins >> enrollment >> self enrollment
You can set to unenrol users after they are inactive for a specific period of time. http://docs.moodle.org/22/en/Self_enrolment#Unenrolling_students_who_haven.27t_been_active_on_the_course
or perhaps the cleanup settings http://docs.moodle.org/24/en/Cleanup