threadnecromancer,
I don't think it'd have to extend the Great Patriotic War to keep the Red Army out of Manchukuo and northern China. Stalin could just be a touch more paranoid that the WAllies were requesting the Soviets join in against the Japanese in order to weaken his troop numbers in Eastern Europe as part of an invasion plan of theirs. Or the Red Army could've suffered slightly higher combat losses that left it just a tad too weak have spared those troops. Or perhaps the deals the WAllies were willing to make with Uncle Joe just weren't juicy enough for him to agree. The end result being no Red Army attack on the Imperial Japanese Army across the Soviet's far eastern borders.
I still think the two Atom Bombs would've been enough to have pushed the Japanese into acceptance of their defeat.
For the sake of argument though, let's say it didn't. Or that the Emperor's Surrender Recordings were successfully intercepted and destroyed by LTG Mori resulting in a coup that ended any immediate hopes of surrender. Then, without any third Bomb being immediately initiated over any Japanese target, the Imperial War Council - reformed with some new faces on it - convinces itself that the Bombs were but a "one off" and that Japan could, somehow, endure any more the US came up with - if it ever could.
Thus plans for Downfall continue. In the meantime however, the naval blockade of the Japanese home islands continues to tighten and thus prevent the shipment of foodstuffs in too many regions of Japan. Even today, cargo ships are a preferred means of getting foodstuffs to quite a few Japanese towns otherwise lacking sufficient road or rail connections. In the summer of 1945 it was even worse. Stop those coastal transport ships and famine will quickly become "a thing" for the Japanese by the fall of 1945. It certainly would've settled in by November of that year.
Perhaps the Japanese would've come to their sense by then. Perhaps the Allies would've realized that the blockade would be better for them than feeding entire divisions of Allied troops into the killing grounds the Japanese had made of all the viable landing sites on Kyushu.