But this is the point, if the financial assistance from the government isn't provided, NSW can't lockdown for much longer. There will be no choice but to open up, as other countries overseas have done.
I really do think you're underestimating the bad blood that would exist if this were to occur, both between NSW and the commonwealth for lack of support and NSW and the other states if they closed their borders.
The wheels would have fallen off and all sense of order you assume will be gone.
There is no way the commonwealth would allow this situation to occur, especially in an election year. They will be wheeling and dealing to "make lemonade" as you suggest, and if that means using NSW to restart international trade and travel, I think it would certainly be possible. It all depends on what NSW wants to do - they may not want it either. But with trade to the rest of the country strangled, we're going to need other markets.