Mo. Rev. Stat. § 41.300

An officer who desires to resign shall submit his resignation to the governor, whose action thereon shall be final. The governor may refuse to accept the resignation when the officer is under investigation, under charges, awaiting results of trial, absent without leave, absent in the hands of civil authorities, in default with respect to state or federal funds or property, in time of war or when war is imminent, in time of civil stress or emergency or on account of exigencies of the service.