Final answer:
In the event of appointment termination, it is the responsibility of the insurer to notify the producer. This notification is often required by state insurance regulations.
Step-by-step explanation:
The individual or entity required to notify the producer in the event of appointment termination is D) The insurer. In insurance terms, the producer often refers to the insurance agent or entity that has the authority to sell insurance policies. When the insurer decides to terminate the appointment of a producer, they are typically required by state insurance regulations to provide notice of this termination both to the producer and the state insurance department.