OTL, The Japanese actions were due to the emperor’s wishes rather than military defeat. The Kwantung Army was undefeated, and retreated back to the well fortified tunghua line. The Japanese planned to use chemical and bio weapons against the Soviets. The Soviets meanwhile had logistical difficultly operating in the Far East. The Americans expected 600,000 Soviet casualties, while Soviets themselves expected 1 million. How would the war in Manchuria look like if Japan didn't surrender after the nukes?