In the event that the State of Nebraska, an adjoining state, the government of the United States, either, any or all of them, should agree to take over any bridge acquired by a city of the metropolitan class or in course of construction under sections 14-1201 to 14-1252 and thereafter maintain and operate such bridge as a free bridge at its or their expense, then such city is authorized to convey such bridge on such conditions to such party or parties. Such conveyance shall not be made unless and until all outstanding bonds issued to finance the bridge have been paid and canceled.