If, upon the deaths of a retired member and, if applicable, a designated survivor, the total monthly benefits paid to the retired member and to any designated survivor do not equal or exceed the retired member's accumulated contributions at the time of his or her retirement, the difference shall be refunded to the person designated in writing by the member or the designated survivor, whichever was the last to receive a monthly retirement benefit under this Code section. If no person has been so designated, the amount shall be paid to the estate of the member or the designated survivor, whichever was the last to receive a monthly retirement benefit under this Code section.
OCGA § 47-23-84