how to remove a customer account (but there are active agents SD)?

how to remove a customer account (but there are active agents SD)?

We finished working with one customer. 
Unfortunately, we can't uninstall SD agents in the company now.

How I must remove the assets assigned to this customer / account (reduces the license Number of Assets)  ?
How can I delete the account, but to I want to see the history of the requests and works log for this customer account ?
                New to ADManager Plus?

                  New to ADSelfService Plus?