(a) a person has, in the performance of the duties of an office, made a migration decision; and
(b) the person no longer holds, or, for whatever reason, is not performing the duties of, that office;
this Part has effect as if the decision had been made by:
(c) the person for the time being holding or performing the duties of that office; or
(d) if there is no person for the time being holding or performing the duties of that office or that office no longer exists--such person as the Minister specifies.