What would have happened if Hitler failed to remove democracy?
He would have been voted out. The massive rearmament program would have bene impossible. And the financial flim-flam that hid the size of the deficit would have caused serious economic problems.
But the question is unreasonable.
At Hitler's core was dictatorship, concentration camps, war, and genocide. It is impossible to separate those from Hitler.
If Hitler had failed to undermine the democratic process in the Weimar Republic, he would eventually have lost the chancellorship and retired to the bank benches. If parliamentary democracy survived the challenges of the Nazis, they would have begun to steadily lose electoral support. In a parliamentary system, you need to control the legislature, through majority rule or coalition, or in the case of Weimar Germany receive an appointment by the President, to control the government. Hitler was awarded the chancellorship because the Nazis never achieved a majority. It would have slipped from his grasp as the economy gradually recovered from the Great Depression and the real parliamentary parties began to recover electoral support.