If any member withdraws from the retirement system prior to retirement the total amount contributed by him with such interest as may be credited thereto, shall be returned to him, provided, however, that the board may prescribe the terms and conditions upon which a member, whose district service has been terminated except by death or retirement, may elect to leave his contributions and interest thereon in the retirement fund, and the terms and conditions upon which a retirement allowance may be made to him after such termination based upon his contributions prior to such termination.