Where the proposed district involves expansion of the boundaries of an existing twelve-grade district by addition of non-twelve-grade territory the board of education of the twelve-grade district shall continue as the board of the enlarged district.

   Where the proposed district involves the merger of 2 or more twelve-grade districts with or without the addition of non-twelve-grade territory, or where the proposed district involves merger of non-twelve-grade districts into a new twelve-grade district a board of education fairly representing all areas of the new district shall be appointed by the intermediate district board to serve until a new board is elected as provided in section 410 of the school code.