Couple of points:
Soviet Union lacked critically (just to mention couple of natural resources) rubber and copper. Without Allied shipping many many many things would have not been build in Soviet Union - and furthermore, without getting these natural resources from outside, Soviot Union must have guided a LOT OF RESOURCES to finding/mining/producing/refining these resources or their alternatives.
Over 50% of aluminum used in Soviet Union came from UK/US. Without this, Soviet aircrafts would have be build out of snow, or some material like that.
Soviet Union build just 265,000 trucks. US shipped in 409,500 trucks with no trouble. And you have to remember that soviet trucks were old inefficient useless models - while american trucks were the newest efficient models available.
1942-1945 Soviet Union produced 92 locomotives, allied shipped in almost 2000 locomotives. Without these, the Soviet Union wouldn’t have means to move around troops, not to mention move around food to people - without food - well, I’m under the impression that even soviet people need to eat.
In 1941 Soviet Union produced 30,000 railcars, 1942-1945 ONLY 1087. This would have meant COLLAPSE of food delivery, but luckily allied shipped in over 10,000 railcars.
Soviet Union didn’t even bother to produce rails, I mean, how in the world they thought they were gonna move their trains around? But luckily allied shipped in over 90% over soviet rails.
Over 35% (latest figures from this centery) of explosives used in Eastern Front came from US and UK. Obviously Stalin think about blowing up german Tiger tanks with potatoes, but luckily allied helped him out - it’s a lot easier with explosives.
And let’s take a look at soviet food situation: pre-war Soviet Union had troubles at feeding it’s population. End of 1941, Nazis had capture 40%-80% of sugar, pigs, fields, grains… Let’s say Soviet Union had 50% of it’s food resources left. After army took away tractors from farms, and Soviet Union didn’t produce too many tractors, (add to that the fact that best male population was in the army) possibilities to actually make good usage of that 50% of food resources was low. Let’s say soviet workeds miracles and 85 years old grand-mothers were as strong as tractors, and they managed to use 35% of food resources. Now, how on earth you are going to transport that food around Soviet Union to civilian population and to troops at frontlines - Because Soviet Union didn’t build locomotives, or traincars, or even rails, or trucks…? Add to that a very cold winter, looting, chaos, and the fact that frontline troops were in prime position for getting the food.
Considering above, how on earth do you see Soviet Union making it without allied support without totally collapsing due the lack of food?
State where country produces 10-50% (depending how you crunch the numbers) of needed food per year, is simply not sustainable several years.
Even thou Soviet Union always felt good about the production evacuation, it wasn’t all that great. A large amount of factories were lost. And, it took a looooooooon time to soviet production to start a work again - pig iron production fell 60-70%, steel production fell 50-60%, coal production fell 60% comparing 1942 to 1940.
Compare all this to Nazi Germany where military production was just a tiny percent of all production (mostly civilian production) and you start to see that behind all the aggressive boasting nazis weren’t ready/prepared/geared up for a war.
Personally I think that Nazi Germany would have easily conquered Soviet Union if:
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Hitler would have prepared german production for war.
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or Allied had not supported Soviet Union.
… I know it’s not a very popular opinion, but after a decade of number crunching I feel that way. 
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