Clearly they would not have. Unless the hard winter alone would have crushed the German Army.
There were moments when the Soviets would have lost without American aid, but their war industries weren’t terrible and Stalin was prepared to lose tens of millions to win the war. If they had been able to get through their weakest moments, they very well could have won without our material aid. But our opening up a second front in Europe insured that Hitler would be denied victory.