Without American entry, the Axis unquestionably defeats and the USSR and then fights the UK to a stalemate at absolute worst. To quote from Denis Havlat's articles on Lend Lease, part 2, from the
Journal of Slavic Military Studies:
Overall, the Western Allies were responsible only for a small fraction of the losses sustained by German infantry and armor between 1941 and 1943 (around 10 percent); however, their contribution in the destruction and occupation of the Luftwaffe was overwhelming. The same applies to their contribution in forcing the Germans to leave most heavy artillery in the Reich as anti-aircraft weapons, preventing them from being used as anti-tank weapons in the East. Without Allied military intervention, the Germans could have sent at least 2,000 additional tanks, some 5,000 additional 88 mm anti-aircraft guns, around 15,000 additional aircraft, tens of thousands of additional motor vehicles, and up to half a million additional soldiers to the Eastern Front in the years 1941–1943, which would have shifted the balance in their favor.
Further on:
Without the need to fight in the Atlantic; to transport large amounts of troops, equipment, and supplies across the entire continent; and the necessity to defend against Allied bombing, Germany could have massively reduced its U-boat, locomotive, and anti-aircraft gun and ammunition production and converted at least part of these capacities into the production of more aircraft and equipment for land warfare. Additionally, without bombing, and the need to maintain a large enough army to fight on several fronts, there would have been less need to use forced labor in the factories, thus boosting production. Historically, Germany already outproduced the USSR in certain areas like locomotives, trucks, and even bombers, with 12,664 produced by Germany in the years 1941–1943 as compared to 11,359 built by the USSR.170 Without Allied intervention and Lend-Lease, Soviet margins in these areas would most likely have widened, while margins in areas such as tanks would have shrunk significantly. If Germany and its industry could have concentrated on one single front from 1941 onwards, it most likely would have vastly changed the outcome of the war in the East.