Question is, even with a Hapsburg defection from the war (and this would infuriate the Germans no end, since it was Hapsburg assertiveness in delivering ultimata to Serbia that started the whole war up) will they back out soon enough to save their Empire from disintegrating?
No question that if AH tries to stay loyally in the war they started to the bitter end, it will disintegrate; the Allies, despite Russia's defection, have promised independence to too many factions not to insist on it if AH is at their mercy.
Quite aside from Allied insistence though, the war as conducted OTL was terribly corrosive. Consider Tito for instance; he was not in the pay of nor aided by Entente interests to subvert AH; he was a young man of no general note from a mixed marriage who was drafted into the AH army. The Russians, who were generally defeated badly by German forces, often triumphed over AH ones and Tito's unit was captured. It was as a Russian POW he was exposed to Bolshevik ideology and was converted into a staunch agent of the Comintern. By no means did all captured AH soldiers turn Communist nor did all Red AH subjects derive from such a background, but it illustrates the basic weakness of the Empire. Without a POD to strengthen its internal organization prior to the war (and I have searched in years largely in vain for a plausible one) the Empire cannot stand for long without being torn apart at the seams during battle; toward the end only the support of Germany was holding it together.
Give me a German Great war victory, even such a mild one as merely getting a "White Peace" truce with no territorial gains and no restoration of colonies, and I will give the AH Empire fighting odds to be kept alive on life support, because it would be in German interest to attempt this. I am not sure they could succeed though against the discontent of the divided but numerous non-German, non-Magyar people who composed the majority of subject peoples, not after they'd witnessed the failure of their armies.
OTOH with that elusive POD to strengthen AH so that their forces could hold against Russian ones--not necessarily win any great victories, just stand against the hammering--and such a more solid AH corps would surely do better against such foes as Serbia--then the better performance of the CP in the East ought to be a possible factor in getting a peace earlier, an acknowledged stalemate in the West leading to cease fire and status quo ante there (more or less; assuming the Germans did invade through Belgium then they might get away with more or less puppetizing that kingdom since its neutrality stands revealed as a farce--a net loss for the Allies then. Russia might have to concede territory to the Germans in the North, which might wind up being set up as more puppet kingdoms so all this amounts to mild CP victory, with AH doing well to hold is own (may well annex Serbia, though that would probably prove to be a colossal mistake). With such an early mild CP victory Bulgaria may hold its annexations of Thrace from Greece and so forth.
But I think the only way AH survives is with German support and so their best move is not to start the Great War at all, which was IIRC Berlin's advice to them too.
If Germany is defeated, even less abjectly than OTL (say, conceding Alsace-Lorraine to become a neutral buffer state, but not being required to disarm to the low levels imposed OTL, not being subject to the high reparations and suffering no more territorial losses) then AH is doomed I think. Without a war it might limp along without much German help, maybe, but if its basic governance does not improve markedly it could disintegrate even without a war to stress it.