Scotty from marketing is fond of saying they won't be allowed into the country before 4 March. Whether it's legal to deny access to the country to Australian citizens is an interesting question. The NT quarantine in the mining camp may be being achieved under 'national security' laws not health laws*. In which case, I think we all have a lot to be afraid of if they can call anything they like 'national security' and deprive people of their liberty on flimsy excuses like "we're not entirely convinced" that you might not be ill, despite testing negative and passing a health exam before we even let you on the QF evacuation flight.
*At least not under NT Public and Environmental Health Act which would require a public health emergency to be declared before it would be legal to detain anyone. As of yesterday, no such emergency had been declared in NT. IMO it would be a farce to say there was a public health emergency in NT even when the pax arrive.