Once you get into this sort of scale you can expect serious attention from customs and the AFP. It's worth putting up major surveillance and using informers when you're talking about hundreds of kilos. This guy must be praying to get sent back to Australia, being someone's bitch in a PNG prison for the next ten years wouldn't be pleasant. An engineer from the company which did our maintenance up there did a short spell inside after being caught with a small quantity (personal use) of the local wacky weed, every time his mates went to visit him he was in tears. There are plenty of films and books about westerners who spent time in Thai prisons and the appalling conditions, I would choose a Thai prison over a PNG one every time.
Back in Australia he would probably be facing conspiracy charges and matters relating to his departure. On "Border Security" most of the smugglers caught with around 300 gms of heroin seem to cop a 6-7 year stretch. Even if he gets 10+ an Aussie prison is like a 5* hotel compared to a third world prison.