The Attorney General, Secretary of State, Treasurer, and Controller shall, in addition to the appointments required to be made by Section 12701, designate the order in which persons holding office as their deputies or assistants, and not appointed under Section 12701, shall serve as their respective successors in the event that such officer and the successors appointed by the officer under Section 12701 are unavailable as a result of disaster. If any such officer and the successors appointed by the officer under Section 12701 are unavailable as a result of disaster, the powers and duties of the officer’s office shall devolve upon one of those deputies or assistants in the order designated and that person shall declare that that person is undertaking the duties of the office and take and subscribe the oath

therefor; provided, however, that any such deputy or assistant may declare that that deputy or assistant is undertaking the office and take the prescribed oath if none prior in order of succession enters upon the office within seven days after the incumbent thereof becomes unavailable.