Alan Partridge asks: "And what would happen if more than 200,000 refugees arrived? Say 400,000."
Your question is based on an assumption that Australia couldn't absorb a people rush. When gold was discovered in Australia, population tripled in ten years. Few got rich on gold but many prospered from new industries a higher population bought into being.
Your question is based on a 2nd assumption: That refugees are lazy liabilities, not assets. Change your perception and thousands of nation-building assets will appear.