Suppose there is no Hitler--something as simple as he is killed in the Great War. Along comes the crises of the 1930s, but there is no one to take Hitler's place as an organizer of a right wring party that can simultaneously appeal to working-class, middle class, and upper class supporters.
As I understand it Hindenburg favored the restoration of the Kaisers. Might he go so far, in a worsening early 1930s crisis where he can't just put Hitler in charge, to restore the monarchy by inviting in a different royal house than Hohenzollern? Perhaps the Wittelsbachs, or even a Hapsburg? A Catholic dynasty would certainly make absorbing Austria easier and I'd think any lingering anti-Papsim among northern elites would be offset by the desire to bring in a bunch of conservative southerners.
I've little enthusiasm for seeing either Silly Willy or his Nazi son ascend the throne.