The DefaultSyncHandler by default will remove (local) users when they are no longer active in the external system aka no longer provided by the ExternalIdentityProvider. It would be useful to have an option to disable users instead of removing them completely.
This is good for use cases that need to keep the user's data around in the JCR and can't just delete it. Also, we have seen cases where the user is only temporarily removed from the external identity system (e.g. accidentally removed from group that maps them to the JCR system and quickly added back), where a full removal can do unnecessary operations.
(Note: There is an option in the SyncContext interface to suppress purging completely, aka they won't be removed nor disabled, and the JMX sync commands such as purgeOrphanedUsers() "use" it. However, the JCR users look like "valid" users then locally. Even if the authentication is done completely through the IDP and will fail properly for these missing users, it can be difficult for other uses like administration, monitoring, other application code to detect that such a user is not active anymore.)