End date all assets and close the type on the metamodel form so no new assets of that type can be created.
The asset type is no longer valid and no new assets of this type will be created. The assets and asset type will be accessible when setting the effective date back.
Use the Delete Global Assets form to close all assets regardless of location which are of the type being closed. Be sure to select all XSP types and move only the asset type being closed to the CLOSE area of the screen. Deleting assets is possible - no history will be maintained when deleting. NOTE: Contact Bentley Support if the asset type being closed is hierarchical.
To confirm, set the effective date back and query assets of the type just closed on the Asset Items form.