Much like the federal government, which has enacted the Uniformed Services Employment and Reemployment Rights Act (USERRA), many states have enacted laws to protect the employment status of the men and women who serve in the armed forces (38 USC 4301et seq.).
Missouri has enacted such a law for public employees.
Remember that USERRA, a federal law, preempts any state law that is less protective of the employment and reemployment rights of uniformed service people. That is, if Missouri law is less protective than USERRA, then the rights given by USERRA will apply and not the less protective Missouri law. In addition, if Missouri law is more protective than USERRA, then the Missouri law will apply.