We’ll say that magic happens-the Japanese would have surrendered by regular bombing before the planned invasion, even without the atomic bomb. So I’ll say that five nuclear bombs would be ready for tactical use.
I think the Allies would have lost 1.5 million men, including naval losses, radiation poisoning after entering area attacked by atomic bombs, and regular land fighting. Countless more would have been wounded. This also includes Soviet losses from the planned Soviet invasion of Hokkaido.
The Japanese would have lost at least 12 million men killed, due to the enormous losses fighting, from the nuclear bomb, and the mass of Kamikaze attacks. This total includes PCFC losses. 1 million more might have died in guerrilla warfare after the war.
20 million would have been wounded, if not more.