Seriously, - this debate has taken place (basically) many times before with Boroda in the lead.
My eye on it is that the Soviets would have lost to the Axis if not having at least one of the western Allies in the pool. Maybe they would have lived to 1942 or 1943, but IMHO not any longer.
Biggest factor of a chain reaction is probably the British decision NOT to accept Hitler's appeal to reason in 1940.
Had they done so, well here is a possible speculation with the UK at peace with Hitler...
1 Germany now has their full strengthvs the USSR
2 Germany has trade with the USA
3 Japan has possible trade with the UK's colonies (nullifying the embargo effect from the USA, thereby eliminating the "need" of war with the USA)
4 With Germany invading the USSR, Japan becomes part of it with its full strength
5 USSR has a 2-front war
6 Axis has no war in N-Africa
7 The black Sea is open to Axis Naval power, including Japanese!
8 Axis has no attrition on the home front
9 Axis has full airpower
Would be interesting to have a scenario on this one....