What would the USSR have looked like if Stalin in never existed? Assuming everything goes the same way during the Revolution, what would have happened after Lenin died? I don't think Trotsky could have realistically succeeded Lenin, since he was hated in the Party. Would somebody like Kamenev, Zinoviev, or Bukharin have come to power? How would WWII have turned out? What about afterwards? How would the rest of the early 20th century look for the USSR?
We can make it simpler. In 1921 Stalin dies peacefully after an excess of card cataloguing, pipe smoking, and drinking with friends at night.
Basically you're asking whether the 1930s were "intentionalist" or "functionalist." If we follow Ðilas, they were "functionalist." The question then is—what heights will the purges reach without the particular character of Stalin? The answer must be, something more awful than Yugoslavia's indigenous purges, but simultaneously less horrific than 1936-1939's dizziness with success.
They're still awful, unless there's a proletarian revolution in the early 1930s before mass industrialisation sets in.
Scissors, urban spontaneous expropriation, purges of individuals in order to secure advancement, bottom up purges, and a thorough-going attempt at party-renewal by "new" bolsheviks will almost certainly occur. (Fitzpatrick, Ðilas).
yours,
Sam R.