No, in October 1918 what they do is not called fighting, basically the italian army rolled over them, they were hungry, very tired and with little supply and the Italian not...and the idea of eating with what found in occupied Veneto is almost ASB as during the Caporetto retreat the italians applied a policy of burned earth (plus the territory was very poor from the beginning) and what little left was already been consumed by 1918.
They were "rolled over" because of what had happened in Macedonia, where the collapse of that front led to the Hungarian units demanding to go home to defend their southern border. This of course led to a rapid disintegration. Until then they were still resisting, and of course it would not have happened TTL, since given a CP victory the Balkan Front will presumably not have collapsed.
As for "Venetia", I presume you are referring to the little bit conquered after Caporetto. I wasn't. The OP assumes an outright CP win, at least on the Continent, so both France and Italy have collapsed and sizeable chunks of both are under CP occupation. Even if the Austrians can't manage this unaided, once France has fallen the Germans will be free to send whatever support is required.
But i sense that you have not understand what i mean, so i will try to explain again: At this stage victory is meaningless for A-H, as after any peace will be signed, the soldiers will come back home and the real trouble will begin. By this date, trust in the ruling class is basically zero, the army exist only thanks to German help, the is famine in the entire nation, incredible loss of men (not counting the wounded both phisically and mentally) and the economy will be in shamble, in practice all the problems that the victorious nation of the OTL Entente faced, all in addition to the pre-war problem of the Empire; now how can the goverment of the Emperor realistically survive something similar to the italian 'Red two years'.
Sure, the place is a mess, but why should that mean disintegration? None of the victorious powers disintegrated OTL, and in some ways the ethnic diversity may even help, since if, say, a Magyar regiment mutinies, a Croatian one can be called in to suppress them.
There'll undoubtedly be riots, but no reason to assume that order can't be restored. After all, OTL there were red flags hoisted in all sorts of places (though mostly on the defeated side) in 1919/20, but by 1923 what was there to show for it outside Russia? In the end, law and order won, and I don't see why it couldn't have won in a victorious Austria - especially if the even more victorious German army stood ready to lend a hand if needed.
And remain in the A-H what advantage mean?
And equally what advantage rejecting it? Are people going to rush out and get massacred on barricades just to replace indirect German domination by direct?