By using all it's viable resources, Russia was probably able to hold it's own if totally alone against Hitler at least until 1942. But now considerating the war with the West existed, but not the Soviet Lend-Lease, the Western Allies would be ready to "help" Stalin by their crusade against Hitler by '42. Then, Stalin would be able to take the economy and the military forward like driving a car without oil to run from a muger. All he would need would be conserve strenght in order to be saved by the democracies (of course, this would likely not meant Eastern Europe under Soviet control, and the Soviet economy well broken). So, it's impossible to desconsiderate that actions in the West not changed the things in the East and vice versa (it was a global war, damn!)
Germany actually captured many most of the rich regions of the USSR (apart from oil), and this is were the Lend-Lease comes to be significant with the time, since the Soviets had RESERVES of raw materials and food, and they would not last forever. While Germany and it's Allies, without the naval blockade, other fronts, and able to maintein it's conquests, together with the superior German technology and training of it's military, would possibly be able to defeat Stalin with the time.
Other thing is that the Germans needed oil, and Stalin probably would set fire in the oil fields before they were captured. It would took months from them to put to work again, and the Anglo-Americans would be eager to bomb them after repaired. The US was capable of muster much more strenght against Hitler if necessary, and assume a defensive line in Japan. The US would still be capable of launch a decisive air war over Germany, in which Germany in fact commited most of it's fighter force and was defeated by a wide margin. And ultimately, the Americans had a nuclear edge over Hitler.
In the end, Hitler's life would be by no means easy. However, this was only because the joint Allied effort. Put the Soviets against Hitler alone, and things could had been much different. I also would like to let clear that I'm not saying what I wrote above would certainly happen. They were just some possibilities in my opinion.
Edited by Jenisch, 20 March 2012 - 06:10 PM.