It is impossible to terminate Plesk license attached to terminated subscription, an error message is shown on "Terminate License" button click:
It is prohibited to Upgrade/Downgrade Resources which are not installed; such as <>
The system attempts to place a change order to downgrade Plesk resources, but the subscription is already in the status Terminated/Removed, which prevents any orders placement. The issue is valid for very old subscriptions, terminated in early BA versions (5.0 or less).
Please terminate the license in KA manually and contact Odin Technical Support Team to change the license status in BA.