What would have happened if the US did not drop the atomic bombs on Japanese Cities in WWII?

What would have happened in WWII if the US did not have atomic bombs and there was no bombing of those two Japanese Cities. I suspect that the battle of the Japanese Mainland (including Tokyo) would have killed more people in the long run and the war would have gone on for many years. I understand that even kids as young as 7 were expected to fight against the Americans. Any theories?