Alternative histories are fun, aren't they?
I don't think the German army was in any real state to invade Russia in 1939 and lacked the adequate supplies and equipment to realistically sustain such a campaign. They could not deploy all their reserves to the East to support such a move as a large number of divisions would have had to be kept in the west as insurance against a combined British and French assault. Both the British and French armies were large, albeit inadequately equipped, but should not be underestimated. The Russian army was also in a dreadful state, poorly equipped with obsolete equpment and with incompetant leadership following Stalin's purges. (Stalin himself acknowledged this, even in 1940 he gave orders that German reconnaisance planes over Soviet territory were not to be shot down for fear of provoking Hitler). I think any attempt following on from Poland would have got bogged down anyway even utilising the troops that in reality were deployed into France. A German army stuck in a war of attrition would have presented an opportunity that the British and French could have siezed.
Now if the Japanese had attacked Russia from the east and tried to squeeze the Soviets between the two forces then this could have been a deciding factor. They had little armour but large reserves of man power and could have played a key role.
If Germany had somehow successfully conquered Russia at such an early stage then I doubt very much if their armies would have been in any shape to have a crack at the west as many of their depleted forces would have been held down as an occupying force. I think Britain would have been safe for a couple of years, maybe until 1942 or 43 before any real invasion attempt could have been made. Peace would probably have been pursued as with the captured Russian fleets and landing barges, Operation Sealion may have become a viable proposition. (In reality in 1940 the Germans were woefully under equipped to undertake the invasion, despite the public perception to the contrary. They intended to send 27 divisions in Rhine barges pulled by slow tugs across the Royal Navy dominated Channel with the RAF far from beaten. Wth the RN decimating the cross channel supply lines, it would have been a reverse Dunkirk scenario even if they had somehow formed a beachhead).
Maybe I'm talking drivel, not sure.
