Probable internal war within the elite of the politbeaurau; whether any of the 'great and the good' would have had the personality to dominate is moot.
Whoever succeeded Lenin - I'd have thought Malenkov - would have continued his slightly softer forms of Soviet Socialism; perhaps the pogroms of the 1920's might have been limited, the military not emasculated by most of its' officers being executed - and it might have been stronger by 1939, limiting Hitler's insane ambition - and possibly threateming these islands with the invasion.
Howzat for speculation?