If a disability beneficiary is restored to service, the retirement allowance of the beneficiary shall cease and the beneficiary shall again become a contributing member of the retirement system. Anything in this chapter to the contrary notwithstanding, any prior service certificate or creditable service which was used to compute such a member's creditable service at the time of retirement shall be restored to full force and effect, and upon the member's subsequent retirement the member shall be credited with all service as a member.