What would happen to Australia if it were cut off from the rest of the world?
If we aren't trying to imagine a nuclear holocaust, and the rest of the world just decides to punish Australia for some reason or another, it would cause problems in the short term at least. Australia imports all of its oil, and has no nuclear power plants. So within a few months, there will be no electricity. The government is likely to ban cars and public transport to ration fuel. New coal plants will be constructed, and investigation will be done to copy South African technology to convert coal to oil.South Africa has a way to make oil from coal. Simultaneously, renewable energy sources will be given top priority.
Australia is self sufficient in most vital areas, but it will have to do without some technology. Mobile phones for instance, will become outdated quickly, as Australians will have to maintain what they have. Car technology would fall behind, as would simple household goods like fridges, washers, etc. The nation would eventually catch up and become self sufficient where it counts. After all ig North Korea can do it, why not Australia?
If the scenario is a nuclear holocaust, then Australia, or at least some parts of it, would likely be some of the few places to survive the exchange. The cities would likely be targeted, but the interior is so huge it would likely survive unscathed. It wouldn't be a stretch to imagine a scenario like Mad Max playing out.
EDIT: Changed "Energy " to "Oil" in the first paragraph to remove contradiction where it conflicts my statement that Australia will need to reinvent the South African coal to oil conversion process.
We would still have plenty of food. We have the raw materials to make pretty much everything we want.
We would have to re-establish a few manufacturing industries we have let slip away over recent decades. We certainly have the expertise and knowledge to do it. But it would make the cost of those products very high, at least initially, so we would probably go backwards with the standard of our cars, white goods, and technology for a while.
Clothing would become a lot more expensive, so people would have to relearn some old skills like darning socks.
I would personally miss the chance to travel the world.
We would no longer get to laugh or groan at Donald Trump's latest idiocies.
I think Australia would be fine without e rest of the world. I'd miss their cultural influence on the rest of us, but they ma be prosperous despite contact with the rest of the world. whether their technology would advance beyond ours or lag behind during this succession is still questionable, but can you imagine what great cultures and influences it might bring once we reintroduce it to the world in 500, 1000, or 5000 years?