Did you ever wonder what happens to those Powers of Attorney when your CPA retires, dies, closes their practice, fire you as a client or you fire them?
If nothing is done the government keeps acting upon your initial request.
If possible the practitioner should withdraw the representation of each client. Otherwise your information will continue to flow to that address of record until the issues are resolved, enough time passes or you notify the IRS. But under Circular 230 the CPA owes responsibilities to the client (which can be billed).
Client should not always rely others to make these changes they should take responsibility in certain situations particularity if their CPA dies.