Considering the stationing of US Marines in the NT, does anyone truly believe that in the foreseeable future we could be without topline US air support? Any scenario that involves Australia being in combat in SE Asia would surely involve some kind of "build up" or show of force, as a deterrent effect. That would likely involve US F22s arriving on Australian soil within a few days of any emergency. That's part of the beauty of having powerful allies stationed on your soil.
and it isn't like we requested them to be there. By the sounds of it it was the American government that were very keen to have more American troops in Australia so in theory this should just be an upside to us letting the Americans station more troops here.