I know it's not possible to change a username, but how about the email address associated to a user account? The domain is no longer available, therefor no emails can be received for that address.
I assume the answer is "no" since I saw the field was not editable. Next, I assume that I will have to create a new account and abandon the current one, including all the history if any (so much for data integrity).
Presuming that I am correct, you may want to re-think the benefit of this rule because companies churn all the time - they come and they go. Does it make sense that those accounts do also?