QAC does not allow any user to be fully deleted from the system. Currently, deleting a user results in the "Active User?" field not haveing a green check mark. The reason behind this is maintaining historical record if someone created, ran, or otherwise modified anything within the system.
What if you have an account that never executed tests, created tests, etc; i.e. not associated with the historical record of any object? In my case, I created a test account to try the security configuration after making changes, but prior to exposing end users to them. If I no longer need this account I would like to remove it entirely.