In the event that USSR surrender to Germany in 1941-42, were allies planning liberation of Europe and USSR? Or was invasion US/UK/Canada only possible if Soviets were successful, therefore no such plans were ever made? Things got pretty close in Liningrad, Moscow and Stalingrad. If one or more of those Soviet centers fell, it was possible that Soviet defense and moral would collapse and country could surrender or be occupied by Nazi invaders. Were Allies preparing steps to liberate Russia and the rest of Europe from Nazi occupation or the only hope was Russia to defeat Germany on Eastern front? Or did Europe's liberation depend 100% of soviet troops?

I am curious since the D-Day invasion was only attempted in June of 1944 and after a series of crashing defeats that Nazis have suffered in Eastern Front, was D-Day still reviewed as possibly if Nazi Empire stretched from Brest to Ural Mountains? For sure strategists in UK and UK were reviewing all possibilities and scenarios?