When deleting a customer is there a way to delete all related activities such as notes, activities and opportunities without orphaning them?

When a customer closes an account with us after a period of time their account purges from our banking core.  On a nightly update if it is no longer found in core, the update process will delete the customer from the CRM customers module.  That leaves all the notes, activities, opportunities etc. orphaned with no related customer.  Does anyone have a best practice, or method for how they deal with this?  Thanks in advance.