And this is the point most people don't get. An invasion would have killed more Japanese than the bombings, and completely shredded what was left of the country.
We had total mastery of the air. Before one soldier put a foot on the Japenese home Islands we would have systematically destroyed every Japanese city with high explosive bombs and fire bombings. We had already firebombed Tokyo with the loss of about 90,000 civilians. We would have done the same to all cities. Oddly starvation and disease would have killed more than our bombing.