Can't happen. The Japanese had already decided thatr a war with russia would be a bad idea. Nomohan and all that. The Soviets are also unlikely to surrender. Agree to a peace? Yes. But an outright surrender, including the loss of Vladivostok to Japan, is on the same level as the sea mammal which shall not be named.
And anyways, something tells me the US takes it back. I mean, by 1945, American combat power was huge. Sure, they can open yet another front, keep japan guessing, and set up B-29 strikes on the home islands.