If in the event of an attack any officer named in Subsections (a) and (b) of Section 6-139 and any duly authorized deputy is unavailable, his emergency interim successor highest in rank in order of succession who is not unavailable shall, except for the power and duty to appoint emergency interim successors, exercise the powers and discharge the duties of such officer. An emergency interim successor shall exercise these powers and discharge these duties only until such time as the lawful incumbent officer or any duly authorized deputy or any an emergency interim successor higher in rank in order of succession exercises, or resumes the exercise of, the powers and discharge of the duties of the office, or until, where an actual vacancy exist, a successor is appointed to fill such vacancy or is elected and qualified as provided by law.