The success of the Sickle Cut Plan made everyone crap their pants. Including Hitler and the high command German generals. It was basically the Schlieffen Plan turned on its head with a high risk armor movement through the Ardennes. The French and BEF played into it perfectly by rushing to the Dyle line which let Guderian cut off their escape. It scared Hitler so bad (he was not thinking beyond Sedan) that he ordered a halt right as the German armor was getting ready to go for the kill at Dunkirk.
You’re right though. If it had not been so successful and instead became a protracted war of attrition who knows where the boundaries of the Iron Curtain would have ended up.
My guess, the Atlantic Ocean.