Hitlers real goal was neither the UK, France or Poland. His main goal was the Soviet Union. He would never have stopped after Danzig, because everything he did was focused on creating german Lebensraum in the east.

He might have made peace with the UK, France, the BeNeLux or the US, but he would have never agreed to an independant Poland. Without Poland at least being a german puppet he can't send his armies east, but he needs to if he wants to defeat Communism and secure the fertile lands of the ukraine and the oil fields in the caucasus.



On the other side: Austria, Sudentenland, Bohemia and Memel all weren't a red line for the western allies, because these were all territores Germany could set some kind of claim on. All were an integral part of either the German Empire or Austria-Hungary just a generation prior, but Poland as a whole would never have been aggreeable to anyone, while just Danzig was never going to be acceptable to Hitler.