I'm assuming our Navy would harbor there when other ports were gone.

Maybe the Australians wouldn't allow that?

I guess I always assumed they would. Kind of like North Korea with Russian warships. I don't think we could take the chance that the Russian naval assets harbored in N Korea were harmless. Likewise, I'm assuming Russia wouldn't be able to make the assumption that American warships harbored in Australia were harmless.

I don't know? Maybe everyone's naval ships just surrender or something? I doubt it though. Your nation being destroyed is, in my mind, more reason to fight in those circumstances, not less.