(1)    Unless the articles of incorporation provide otherwise, and except as provided in sub. (2), if a vacancy occurs on the board of directors, including a vacancy resulting from an increase in the number of directors, the vacancy may be filled by any of the following:

      (a)    The shareholders.

      (b)    The board of directors.

      (c)    If the directors remaining in office constitute fewer than a quorum of the board, the directors, by the affirmative vote of a majority of all directors remaining in office.

   (2)   If the vacant office was held by a director elected by a voting group of shareholders, only the holders of shares of that voting group may vote to fill the vacancy if it is filled by the shareholders, and only the remaining directors elected by that voting group may vote to fill the vacancy if it is filled by the directors.

   (3)   A vacancy that will occur at a specific later date, because of a resignation effective at a later date under s. 180.0807 (2) or otherwise, may be filled before the vacancy occurs, but the new director may not take office until the vacancy occurs.