I think there's a decent chance the Allies would've just allied (lol) with Nazi Germany, and Fascist Japan, seizing this opportunity, would completely focus on Hokushin-ron, invading Mongolia and the Soviet Union through Manchuria. The Allies would mostly sell weapons to Nazi Germany and Fascist Japan before directly intervening once the Wehrmacht and the IJA suffer enough defeats. Who knows, maybe the US would've nuked a Soviet city to force a favorable ceasefire between the Soviet Union and Nazi Germany.