The demand for power in Australia doesn’t get any lower by shutting down a power plant. The only thing that will happen is that the other power plants will ramp up to keep up with the demand. A true solution would be to provide new installed capacity to the grid that would price out the existing assets. And if the new capacity is less CO2 intensive than you lowered the emissions.
Question is what is that other source? If generation of the renewables is lower than peak load (times a reasonable factor like 1.5) than you build renewables. Otherwise you focus on bringing power from hours with lots of renewable generation to the rest of the day aka you build energy accumulation. If the accumulation solution is too expensive (either CAPEX or OPEX) than you have to invest in lowering that down. If you lower that down with your money, it will become more favorable for others to build this solution around the world. Others will come and build this solution of yours. This way you effectively lowered way more emission for the same money (assuming you will come up with something reasonable).