Without Mussolini, maybe the Liberals limp on until they luck out and right the course. Perhaps another rightwing group imposes itself. My bet is on the military staging a coup and taking over. The one thing I don't see happening is communists taking over. The communists simply did not have nowhere enough the level of popular support or coercisive power to take over the country. Hell, even Mussolini's Brownshirts didn't have that kind of power or support. He gained power because the Italian elites (the military, the monarchy, the Liberals) LET him. They could have squashed him like a bug (and they should've), but they lost nerve. However, unlike the conservatives in Germany, Italian coservatives pretty much got everything they wanted, at least until late 30's, so you could say that they did the right thing by humoring him and "letting" him run the country. Until Mussolini gained Hitler's backing, his Fascist government ruled Italy in cooperation with the traditional elites; he never was able to dominate them completely, even with Hitler's backing, and thus it's no wonder that he was the only major Fascist leader to be overthrown by completely domestic opposition without foreign aid. The communists, though, would not have gotten any chance from the traditional elites. If they tried anything like the March to Rome, the military would not have hesitated to crush them and impose military rule over the country.