Retired a while now from Cairns ATC. We had a contingency plan for when either Tower &/or Approach service was not available. I know of 2 occasions when Tower was not available and the plan was put into action. NOTAM issued requiring pilots to phone for a briefing on procedures to follow - e.g. set course time, when to call Approach for clearance etc. Pilots followed procedures well and all worked quite well, apart from longer delays than normal. We also did a post event washup (incl with industry) to ascertain what could be improved. I am sure Gold Coast ATC would have something similar in place.