Oooooohhhhhhh I love alternate-history
Let me see...if WWI and WWII didn't happen.
Honestly, I'd say that Austria-Hungary would've balkanized even if Archduke Franz Ferdinand's United States of Greater Austria plan was implemented mainly because of so many languages and a few religious differences within the Danube Realm. I think the Habsburg monarchy would've remained in German Austria and/or Hungary so we would've seen an Archduchy of Austria, Imperial State of Austria, or the Kingdom of Hungary but whether the Habsburgs would still be the royal family to this day because of those circumstances, I can't say for certain.
I think the Ottoman Empire would've balkanized too because of the exact same problems that Austria-Hungary was facing and we still probably would've seen the Republic of Turkey in my opinion.
I think the German monarchy easily could've survived if WWI never happened, as long as it modernized and kept up with the times.
As long as the 1914 act was honored, I think Irish Independence could've been avoided.
I think the Russian Empire would've balkanized too considering how backward, diverse, and despotic the regime was in that nation. I honestly think that Tsarist Russia was a ticking time bomb by 1914.
I think a royal Yugoslavia might've had a chance had surviving if a proper conclusive Yugoslav identity was established and all of the ethnic and religious groups were respected.
Albania, Bulgaria, Greece, and Romania's monarchies could've easily survived without both World Wars.
I think Otto von Habsburg could have been asked to take the Hungarian throne overtime or maybe a new Hungarian royal dynasty might have been established. Heck, I think a royal restoration could've happened if the 1956 revolution was successful and Prince Otto pressed for a restoration afterward.
Japan's imperial family would probably be a lot more revered assuming if WWII never happened. I think Japan probably could've held onto Taiwan, Southern Sakhalin, the Kuril Islands, and Micronesia without issue but Korea is a whole different matter. I suppose a Korean monarchy restoration is possible in the events of independence and depending on the circumstances and the timing of said independence.
There is no way that an independent Manchuria/Manchukuo, let alone as a monarchy under a restored Qing Dynasty, could've survived easily because of Manchu nationalism being so artificial and the old Qing monarchy being unpopular unless Emperor Puyi really tried and succeeded at being one heck of a statesman and the Japanese actually letting him do what he needed to do in this situation.
Considering that Mongolia was between Russia and China, Mongolia as a monarchy could only survive if Mongolian independence is fully respected, which isn't too likely in my opinion.
An independent Lao and Vietnamese monarchy could still be around and probably be like Cambodia and Thailand depending on how independence happened and how complacent the local monarchies were with the Third French Republic.
The Italian monarchy would probably still be around assuming if the kings were competent and popular.
Spain, this depends on what happens between the wars, and assuming if Franco still came to power, the monarchy might now be restored.
-Frozen Royalist