Mo. Rev. Stat. § 72.340

All ordinances including all ordinances adopted at elections by a vote of the people of the municipality which absorbs the other municipalities shall remain in full force and effect and shall govern in the territory of the absorbing municipality and of the municipalities which are absorbed. All ordinances and the corporate existence of the municipalities being absorbed shall cease to exist and be null and void and of no force and effect upon the effective date of the absorption.