We know the Japanese forces outside of Japan would have surrendered if there was a peace treaty, because that's what happened. That would be the purpose of a p

We know the Japanese forces outside of Japan would have surrendered if there was a peace treaty, because that's what happened. That would be the purpose of a peace treaty (and exchange of prisoners, etc.). If the USSR decided to invade Japan on its own, who cares? We could let them fight. Or we could ally with Japan.