When the returns of an election to pass on the question of decreasing the number of county commissioners in a county show that a majority of the votes cast on the question favored such decrease, the existing board of county commissioners shall continue in office until the time when the terms of office of two members of the board expire simultaneously. At that time, the board shall declare that such two offices are abolished and at its first regular meeting thereafter shall redistrict the county into three commissioners’ districts and shall designate the district which each of the three remaining commissioners shall represent. The terms of office of such remaining commissioners shall not be affected.