Named beneficiaries by members and by former employees; effect of marriage, entry into reciprocal beneficiary relationship, divorce, termination of reciprocal beneficiary relationship, or death

(a) All written designations of beneficiaries for members and for former employees shall become null and void when: (1) The beneficiary predeceases the member or former employee; (2) The member or former employee is divorced from the beneficiary; (3) The member or former employee is unmarried, and subsequently marries; or (4) The member or former employee enters into or terminates a reciprocal beneficiary relationship. Any of the above events shall operate as a complete revocation of the designation and, except as provided in sections 88-84(b) and 88-338(b) all benefits payable by reason of the death of the member or former employee shall be payable to the member's or former employee's estate unless, after the death, divorce or marriage, or entry into or termination of reciprocal beneficiary relationship, the member or former employee makes other provision in a written designation duly executed and filed with the board. (b) Subsection (a) shall not apply to active members who are former retirants who have returned to service. The beneficiaries of retirants who return to service may not be changed except to the extent provided under the retirement allowance option selected by the former retirant when the former retirant first retired.