Maybe less than Col. Landa imagines. With the nearly complete decapitation of the Nazi and Wehrmacht leadership, who will step in and assume control? Unlike the July 20 Plot, the event in Basterds was the random result of two uncoordinated acts of mass assasination, with no plan in place for anyone taking over power in Germany. Even assuming the USA would strike a deal with Landa, he has no authority to negotiate an end to the war on behalf of Germany. More than likely, Himmler (who was not in Paris, I seem to remember) would declare himself Fuhrer and try to use the SS to assume control of the party, government, and Werhmacht. Or, perhaps, a military coup would topple the Nazis. Or Germany would collapse into civil war. Regardless, German resistance in the west would become uncoordinated and ineffective, allowing the Wallies to advance much father than in OTL. Because the Germans would continue to resist the Soviets more effectively out of a sense of self-preservation, it is possible the Anglo-Americans might assume control of all of Germany, Austria, and Czechoslovakia in just a few months
Stalin would see this as further evidence of an allied plot against the USSR and the grand alliance would break up. The wallies might give much more serious consideration for something like "Project Unthinkable" if it appeared the Soviets made it clear they would not accept the Wallie advances as final.
Assuming that somehow a war between the Wallies and USSR was averted in 1944-45, the Cold War would be far colder. However, the main European flashpoint (Divided Germany and Berlin) would be under Wallie control, changing the dynamic in further unpredictable ways.
Once doesn't normally leave a Tarentino movie in a thoughtful mood. Even considering how comically ludicrous Basterds was, it does present some intereseting "What Ifs"