If Italy doesn't get at least Trento and Trieste, there's a revolution in 1919, 1920 tops, and a further invasion of Austria. The historical Vittoria Mutilata was enough to give the country to Fascism in 1922; if Italy walks away from WW1 with the historical million casualties and nothing for it despite being on the winning side, the government that signs the treaty is going to last as long as a possum on the highway.