It's WWI nobody partecipate in that massacres without a traumas and while by a lesser degree (and i really really doubt that WW2 have been a walk in the park), in the end A-H will depend on Germany support as OTL, not considering that in the books is stated that just before/during the second great war there are been big revolt from various minority even with the use of suicide bombers (yes this is a big traumas) and that even if victorious it's far from robust; basically by the end of second conflict the Hapsburg Empire will be a fully owned subsidiary of the German Empire and that will do great things for the legitimancy of current enstablishment.You're thinking OTL, TTL, they won, they beat the russians and them just send support to end the bfrench and british, here they won by 1917 and without Isonzo means less stress(plus Caporetto was a draw till 1918 anyway) and WW2 would be mostly against russia and one ends A-H won two wars without traumas, if a checz legion existed they would have joined the tsar as have nobody to run(USA would extradict them, Canada is USA, and so on), dittto any balkan terrorist, their only hope is...south america.
A-H is stronger that ever here.
Italy relations with A-H will flux between bad and horrible but avoiding two world wars and having a more modern nation system mean that by 1944 Italy will be more stable and rich of his eastern neighbourgh...and this mean stretching his diplomatic muscle, even because the ethnic violence hitting A-H will be a serious concern in many italian political circles.
Regarding who's the attacker in a very probable Italian-Austrian confrontation, well it's hard to say. Italy can rightly sense that the Empire is on his last leg and demand concession and things devolve in a war, on the other hand A-H can try to eliminate the last big problem left or Italy support of balkans and checz freedom fighters will cause a 'punitive expedition'.
Germany reaction is important but also not a guarantee that they come to save A-H, they have just come through a great war fought on her territory, his industrial core greatly hit (the Rhineland) and frankly their neighbourgh seem always in need that somebody save him and by now doesn't look too well. Maybe they decide to stop the plug and divide the empire in something less troublesome.
Btw, Spain while officially of the entente remained neutral during the war, so it's very probable that will find herself at least diplomatically isolated so they will probably go to the only great power not controlled by Germany left