An Enhancement Request has been created to remove all on-prem Exchange attributes using custom policy/attributes after a grace period of x days when deprovisioning Office 365 users.
An enhancement request has been logged for this functionality: 90816.
One Identity Product Management periodically reviews all open enhancement requests and considers them for inclusion in a future product release. There is no guarantee that a specific enhancement request will be implemented in a future release of Quest's products. For more information regarding our enhancement request policy, refer to our Global Support Guide on SupportLink