The Germans are on record as saying that if the Allies had resisted their taking of the Rhineland in 1936 it might have been the end of the Nazis as they would not have been able to stop them, all a big bluff that just made Hitler bolder in the future.
There was another opportunity in 1938. A group of German military officers was planning to oust Hitler in a coup, and they begged Britain to stand up to Hitler at Munich. Their plan depended on Hitler losing face, but his popularity following the deal on the Sudetenland ruined their chances.