It is my understanding that Germany had to detach a division to go rescue their Italian allies who were getting their @$$es handed to them by the Greeks.
That extra division would very likely have broken the Soviets.
If Hitler had not decided to veer south to Stalingrad and instead taken Moscow it’s very likely the Russians would have been finished. But Russia is a very big country and the Russians are a tenacious and tough people. Even if they Germans had taken Moscow they would have been fighting an endless guerrilla war and Hitler didn’t help himself any by alienating the Ukrainians. They would’ve made a great Nazi ally. Hitler had to go bail out Mussolini in Greece in Oct. of 1940.