Vengeful allies might insist on breaking Germany into the dozens of counties, duckies, principalities, monarchies, etc. it was before 1848. I doubt if the most powerful Germanic kings would be allowed to retain their thrones.
Since the Prussian Kaizer was seen as a/the major instigator of WW1, he would be forced into exile and his former kingdom broken up into minor principalities, duchies, etc.
It is debatable whether the Kingdom of Bavaria would be broken up. Other Germans see Bavarian as a bumbling bunch of catholic hillbillies who drink too much beer. Since Bavaria did not start any wars during the 20th century, it might become a confederation of loosely related principalities, duchies, counties, etc. paying - quiet - homage to a ceremonial monarch.
For example, the Bavarian King might attend major parades, ceremonies, etc. but he would sit in the second row, behind the Prime Minister/Chancellor and major ministers. Like the modern British monarchy, he would have the final veto on legislation, but rarely use it.