The Japanese claimed that the Americans would of won without the A-Bomb which suggests that it wasn't necessary to drop it. The Atomic Bomb wasn't even needed because the Japanese wanted peace but not unconditional surrender. There were other options that could have been taken such as invading Japan and allowing Russia to take Manchuria or the continued use of conventional bombing. However, the decision was made a month before the bomb. This meant that their minds
were made up.