The gov decided on the 9TH when the Manchuria Army was crushed. They told the Emperor to accept the Postdam declaration the 10th. It was announced on the 15th.
So, no the bombing was not necessary. Once, they lost their barrier with Stalin; they had no choice but to surrender or to fall to the soviet.
The problem is that the Soviet Manchuko offensive is not even talked about and Japan being nuked is hyped to death.
The reality is that the defeat of the Soviet offensive is what led to the surrender.
Cold war is over:no need to perpetuate lies.