Ah, but don’t foget Europe!
As soon as the US and British armies, supplies, and supply ships and supply dumps were “transferred” from the European front lines (essentially where they were already “opposing” Soviet armies far larger then the US local forces) back across the Atlantic, back across the US continent and then back across the Pacific -
Stalin would have been able to “stabilize” a war-torn and disarmed Germany immediately all the way to the French border. And the French socialist unions and strikers and Vichy government wold have turned France into a Yugoslav or Polish client state.
There are two sets of potential casualty figures; a low number used to gain approval to proceed with the operation ; and a high number used to plan reserve forces, medical needs and, as it turned out, to claim as lives saved by use of the atom bomb. These figures changed over time, starting low and going higher as the enemy build-up on Kyushu was discovered.The invasion of Japan would obviously have been bloodier for the US (which would have been fighting alone) than Okinawa had been. Transfer of additional Japanese troops from occupied China, probably via Korea, would have to have been interdicted, but even with those reinforcements dropping to near-zero, the invasion would have resulted in the deaths of pretty much everyone in Japan just to bring it to a victorious conclusion. We all remember the nutty Rising Sun types who continued to fight for decades after the war ended, because they'd never been told that it was over, and they were only fighting on little ratholes the empire had overrun at some point. An invasion of Japan might have seen primary combat over in perhaps a year, but there would have been thousands (at least) who would only succumb to death in combat or old age.