Even if a simple PoD I think "no lend lease" will be very significant already in 1942. The Red Army was very weak in most of 1942 as most of the men and materiel available in June 1941 were lost and the factories dismantled in the areas now under German control were still far away from full production in the Urals. What kept the USSR from collapsing in 1942 was the reserve armies being raised in deep Russia and which to a significant degree were equipped with lend-lease equipment - that is at least what Kruchtjev and Zhukov said in their memoirs.
The forces raised in 1942 already were much below standard in training and had to be organised along very simple lines because the available officer corps did not yet have the needed skills and experience to handle units more complex than a brigade. In OTL these units usually "vaporised" after a few days of combat but acted to blunt the Wehrmacht meatgrinder. If we add to that an even worse level of equipment (which already was awful) I think it could very well have been the straw breaking the back of the camel.
And even if the "camel" survives a Red Army with no lend lease will be so much weaker that the prospect of pushing the Germans out of Russia appear remote. Not so much counted in number of tanks delivered from UK and USA to USSR (7.000), but much more in all the other items.
If using the "cost data" from this link:
http://knowledgeglue.com/cost-ww2-vehicles/ the 450.000 trucks delivered to USSR in WWII would be equivalent to at least 25.000 T34 tanks. IOW if lend lease hadn't been the Soviets would have produced 26.000 less T34s and missed another 7.000 to produce the 450.000 trucks Lend Lease doesn't deliver. And now we're at logistics 92.7% of the wartime production of railroad equipment by the Soviet Union was supplied under Lend-Lease (incl. almost 2000 locomotives and more than 11.000 railcars). I haven't got cost data on locomotives but I'll guess a locomotive would cost as much as a tank and anyway I think rails were the most important item in the railroad deliveries (ie. steel production capacity). About 50.000 T34s were produced in OTL from 1940 until VE day.
Practically all of the high octane av gas for the Soviets was delivered through Lend Lease. Producing that yourself would have meant a huge and very expensive investment in the Soviet refineries which would have mean less resources elsewhere.
http://www.oilru.com/or/47/1006/
A third of the Soviet wartime aircraft production came from Lend Lease.
https://en.wikipedia.org/wiki/Lend-Lease
At the time when the Red Army went on the offensive it was largely fed by canned food delivered through Lend Lease. Canned food makes the logistic effort in feeding an army incredibly much easier, especially if you are on the offensive.
All in all I would not hesitate to conclude that a Red Army without Lend Lease will either collapse in 1942 as a field army (might carry on as a partisan force) or it will there after have to fight with about half the equipment/supplies it had in OTL and have very limited offensive power.