Members of boards of educational service units existing prior to approval of any plan of reorganization shall serve as board members of educational service units which are reorganized pursuant to sections 79-1206 to 79-1211 until the expiration of their original terms. Such persons shall be members of the board of the reorganized educational service unit in which they reside. Within thirty days after approval of any plan of reorganization by the State Board of Education, the president of the board of each educational service unit being reorganized shall call a meeting of board members of such educational service unit. At such meeting, members of each such board shall appoint one member from each election district to be created pursuant to the plan of reorganization not having representation on such board to serve until the next general election. The board shall take all necessary action to prepare for operation of the reorganized educational service unit following approval of any plan of reorganization by the State Board of Education. Expenses incurred by such board prior to such times shall be prorated between the counties comprising the educational service unit on the basis of the assessed valuation of such counties.