The retirement benefit payable for the month of death of a member, joint annuitant or survivor shall be payable to said member, joint annuitant, or surviving spouse. In the event the final benefit is returned to the System or is not otherwise paid, the benefit shall be paid to the member's named beneficiary. If there is no named beneficiary or estate, the final monthly benefit payment shall be paid to the first of the following:
Okla. Admin. Code § 590:10-7-10