At the end of World War 1, nobody in Germany wanted Wilhelm or the Crown Prince, who was apparently as much of an ass as his dad. You would have had to go down the line of succession to find a good figurehead monarch.
In Austria-Hungary, the empire had only been held together by personal loyalty to Franz Josef II by his subject. He was himself an institution. When he died, the Empire died with him.
Yes, had the royal institutions remained, Hitler would not have risen. But that scenario violates Henkster’s Law.
There’s an irony there with respect to the Austro-Hungarian Empire - the one guy who had a plan to manage its peaceful dissolution was the guy whose assassination started the whole thing, Franz Ferdinand. By all reports his uncle wasn’t too pleased about it, either. If Princip had only missed...