""I know Aus. is a big place, but I can think of half a dozen places you could put down a big passenger jet and there isn't an airstrip within cooee."
and then what..
you think the plane is just sitting in the middle of the outback with 200+ people on board with limited food and water supplies ?"
yep.
You drive out of there in a semi loaded with bullion.
Hardly a chance of being caught - you can be a couple of thousand kilometres away in under two days and have split up the cargo at any time.
A big crime and requiring organisation and funding - but really, the only hard part is pinching the plane - and that may well have been done.
If you want to be nice about it you have a store of water and food for the passengers and a safe with a time lock on it with a sat. phone inside - set for 10 days or so.
Would it be worth it?
well, half a billion bucks would make it happen I suspect. You wouldn't need much if you already had the cockpit team - all you would need would be a handful of others, some bucks and a bit of organisation. Other than the plane, the rest would be a doddle.