When an insurer intends to cancel or not renew a health insurance product for all of the insurer's covered insureds in the State, the insurer shall file a plan of withdrawal with the Commissioner at least 90 days from the date of the proposed cancellation or nonrenewal. When an insurer intends to cancel or not renew all of the insurer's health insurance products for all of its covered insureds in the State, the insurer shall file a plan of withdrawal with the Commissioner at least 180 days before the date of the proposed withdrawal. A plan of withdrawal may not be required for nonrenewal of a contract which was approved for issuance on a single case basis.