Mich. Comp. Laws § 38.2502
A member who leaves office for a reason other than the member's retirement or death, who does not withdraw accumulated contributions, and who satisfies the service or term of office requirements of section 501(1) is a vested former member. Subject to section 501, a vested former member is entitled to a deferred vested service retirement allowance computed pursuant to section 503 or, if applicable, section 13a of former Act No. 198 of the Public Acts of 1951 or section 15 of former Act No. 165 of the Public Acts of 1954, as in effect at the time of termination of the vested former member's tenure in office. The vested former member shall forfeit his or her entitlement to a deferred vested service retirement allowance if the vested former member withdraws from the retirement system his or her accumulated contributions unless the service is reinstated as provided in section 402.
MCL 38.2502