Vulnerability Discussion
Disabling expired, inactive, or otherwise anomalous accounts supports the concepts of least privilege and least functionality, which reduce the attack surface of the system.
Check
Verify the Mainframe Product is configured to disable accounts when the accounts are no longer associated to a user.
If the Mainframe Product is not configured to disable accounts when the accounts are no longer associated to a user, this is a finding.
Fix
Configure the Mainframe Product to disable accounts when the accounts are no longer associated to a user.