What happen in this theater in a hypothical WAllies/Soviet war?
Well, things get worse quickly. With the prospect of battling the Western Allies looming (or arrived) Stalin isn't invading China. Yes it was a rollover OTL, but he doesn't know that it will be, and he will need the soldiers he might lose in Europe. With Soviet forces moving West to fight, well the West, Japan's Chinese forces are free to continue brutalizing the populace, killing tens of thousands more every day. Japan itself is reduced to, if not hell then a reasonable facsimile.
With war in the Soviet Union looming the Western Allies don't bother invading, instead they bomb and blockade the islands to surrender by starvation. Millions of Japanese die in the ensuing months. Even after the government surrenders widespread famine and destruction cause the populace to continue starving as the war in Europe grinds on.
I doubt Japan gets reconstructed after the war finally ends. The Soviet Union will be stuck rebuilding from repeated atomic bombings and the destruction of cities. and the West will be exhausted, and too focused on rebuilding Central and what parts of Eastern Europe are "freed" (a term I here mean bombed and bombarded until muchit resembles the moon).
Of course this is all assuming Unthinkable would be carried out, which is not likely by any means.
Long-term the area is probably worse off. China will be destabilized for a long time to come, civil,war almost certainly lasts longer. Japan will be in ruins