As part of the initial Offboarding workflow used to trigger the archiving process, you can also add a step that removes the Google Workspace license from the user. If the user is leaving your organization, this step is highly recommended as it will allow you to reassign the license.
Once the user's data is in CloudM Archive, it will then only occupy a CloudM Archive license. This license will remain occupied until the user's Drive AND Mail data is purged from the Google Cloud Storage bucket as part of your set retention policies.