Basically, the dual reservoir splits the system frt & rear. It's the differential valve that moves towards the side that loses pressure & blocks the flow of fluid to the failed half
while simultaneously turning the warning lamp switch on. There is no extra safety without the differential valve, You would have pretty much zero brakes the same as the
single "death drive" master cyl. on there now. The rate of total fluid loss would be delayed slightly, but w/o the valve, it still ain't a good place to be.