Mo. Rev. Stat. § 104.343

The surviving spouse of any deceased member who purchased creditable prior service for service in the Armed Forces of the United States pursuant to subsection 4 of section 104.340 and who died prior to retirement may, upon written request, receive a refund of the amount contributed for such purchase of creditable prior service, provided the surviving spouse is not entitled to a survivorship benefit as payable under the provisions of section 104.420.