So, here's the POD: Lenin's Testament gets out somehow, and Stalin gets removed from power.
Assume that the following is true: internal soviet development goes mostly the same (Stalin having cribbed a lot of his ideas from Trotsky), only the soviets have some political power, there is no Holodomor (butterflied away by different approaches to collectivization) and the purges are nowhere near as great. Some foreign capital is infused into the USSR, but they remain fairly economically isolated because of the West's dislike of their ideology, so when the Great Depression hits they recover quickly. Hitler still rises to power in Germany.
Would the Molotov-Ribbentrop pact (or a similar agreement) have occurred? If not, how would WW2 have developed? What would relations between the USSR and the Nazis be like, and how would this have effected Nazi development?