If the proposition under section 19-402 is adopted for the commission plan of government at least sixty days prior to the next general city election in the city, then at the next general city election provided by law in such city, city council members shall be elected as provided in section 32-539. If the proposition is not adopted at least sixty days prior to the date of holding the next general city election in such city, then such city shall continue to be governed under its existing laws until city council members are elected as provided in section 32-539 at the next general city election thereafter occurring in such city.