Hello Neeraj,
GRC takes into account all the objects assigned to the organization unit.
Before deleting an organization unit you must check whether or not these org units are related to any objects that you have moved, old relationships as well as valid from and valid to dates shown in grfn_str_change transaction.
System cannot force the deletion if you have objects linked to the org unit.
Let me know if the information helped.
Thank you,
Fernando