In case of a reversion to a former form of charter or adoption of a new one simultaneously with the surrender of the old, all assets, liabilities and obligations of such city shall become assets, liabilities and obligations of the new municipality, and in the event that a city shall revert to an unincorporated status, the governing body of such city thereupon shall become trustees of the property and funds of such former city and, under such bonds as may be required by the county legislative body, shall proceed to terminate the affairs of the city and dispose of its property.