(a) Upon the death of a member, or if a survivor's pension is payable upon such death, when such pension ceases to be payable, there shall be paid to the designated beneficiary or, in the absence of a designated beneficiary, to the estate of the member, a lump sum equal to the excess, if any, of the accumulated member contributions over the aggregate of all pension payments made. Such contributions shall exclude interest for members covered by the closed plan, and include interest for members covered by the revised plan.
(b) Upon the withdrawal from service of a member who is not eligible for a service or disability pension, his or her accumulated contributions without interest if covered by the closed plan, or with interest if covered by the revised plan, shall be paid to him or her.