(a) Unless the articles or bylaws provide otherwise, and except as provided in subsections (b) and (c) of this section, if a vacancy occurs on a board of directors, including a vacancy resulting from an increase in the number of directors:
(1) The members, if any, may fill the vacancy. If the vacant office was held by a director elected by a class, chapter, or other organizational unit or by region or other geographic grouping, only members of the class, chapter, unit, or grouping are entitled to vote to fill the vacancy if it is filled by the members;
(2) The board of directors may fill the vacancy; or
(3) If the directors remaining in office constitute fewer than a quorum of the board, they may fill the vacancy by the affirmative vote of a majority of all the directors remaining in office.
(b) Unless the articles or bylaws provide otherwise, if a vacant office was held by an appointed director, only the person who appointed the director may fill the vacancy.
(c) If a vacant office was held by a designated director, the vacancy shall be filled as provided in the articles or bylaws. In the absence of an applicable article or bylaw provision, the vacancy may not be filled by the board.
(d) A vacancy that will occur at a specific later date (by reason of a resignation effective at a later date under subsection (b) of section 21-1974 or otherwise) may be filled before the vacancy occurs but the new director may not take office until the vacancy occurs.