Hypothetically, the West allows Germany to take Poland and never guaranteed anything to them, the Molotov-Ribbentrop Pact was signed, and Poland gets divided up between Germany and Russia. In October Hitler decides the West isn’t going to stop him from trying to secure Living Space Eastwards, and makes a shock move immediately betraying Stalin with an invasion of the Soviet Union. No other country gets involved.
Who would win a 1v1 war here?