Without the war to create the hero worship of Stalin, I could see some sort of NKVD coup by the mid 1940s. Although economically more powerful due to the lack of war devastation, the USSR remains diplomatically isolated having no satellite states in Eastern Europe.
Perhaps the Soviet focus moves to Asia? I don't know though. A Soviet Union left to its own devices would by 1943/44 have the worlds most impressive military and could quite easily choose to invade Germany. Theres even significant evidence that Stalin was going to attack Germany in the fall of 1941 or early 1942 (See Icebreaker Viktor Suvorov).
"Suvorov" and Icebreaker have been
thoroughly debunked. The only plan they had was a sketch of a plan for a counter-attack in the event of a German invasion. It was far from a functional plan though. It was literally a sketch on a single piece of paper. "Suvorov" (real name Rezun) also makes, um, some rather weird claims about what certain weapons systems are and aren't useful for.
Also, I really can't imagining the NKVD launching a coup against Stalin. It's important to remember that Stalin had a strong base of support throughout the 30s and crushed anything that looked remotely threatening.
Stalin continues with the Purge cycle.
Purge, rinse, repeat.
Until he'd created the perfect society, yeah. That guy would be purging 'til his death.
But would and could they ignore the USSR? After all the British are going to be paranoid that the Soviets are pushing into Central Asia and "omg if Persia falls, India will be next!" while even the isolationist US was already very paranoid about the specter of communism and meanwhile Japan is fighting a full on war against the communists in China. The USSR, even a politically isolated one, is still a monster with weight to throw around.
The soviets will attempt to reassert themselves in former Russian territories, Central Asia, and China which will cause the other Great Powers to worry about Russian expansion which will give the soviets the excuse to say "look, they're trying to strangle Russia and communism in the cradle, we need a huge military."
Not only that, the various powers will have rivalries with each-other. Soviet help is vital for cutting Japan down to size with minimal cost. The British-German rivalry would mean both of them (and France if it's not a satellite) would be wooing the Soviets. Anyone who didn't like British preeminence over the middle east would have a reason to speak nicely to the Soviets.
Without WW2, I would expect the Soviets would follow their pre-war trajectory and be competing with Japan for the Chinese borderlands, supporting revolution in China (probably Chiang's revolution, not Mao's) and engaging in "red imperialism" which they'd managed to justify to themselves before WW2 changed all the rules. Likely the Soviets would keep foreign Communist parties under tight control, but would not be supporting many revolutions. So... It would be acting alot like the Russian Empire pre-WW1. I think as time went on, people would more and more treat the Soviets as basically just a new Tsarism. Especially if the Soviets don't fight in many wars... In OTL, before WW2, their military record wasn't great so they could easily be dismissed as a threat.
fasquardon