Well, without Benny we have no "Fascism", but we still have a) unruly and revolutionary, but disorganized and divided Socialists likely to create some sort of Biennio Rosso analog, b) disgruntled former soldiers, pissed that all the hell of WWI bought them far less than Italy was promised by the Entente, forming "fasci di combattimento" (sp?), c) a Liberal parliament so corrupt and inept and out of favor with the people that their days are numbered, d) a king who justs wants order so long as it's not "red", and d) major shifts in political thought along divergent lines (authoritarian nationalists, syndicalists, marxists, christian socialists, neo-Mazinians, anti-monarchists/republicans, old skool monarchists etc.).
All the factions and major players other than Mussie that united to become the Fascists OTL are there (Coradini, di Annunzio, Balbo, Farinacci, Grandi, Pannunzio, etc.), as is the Red Menace.
So, we have some massive Red takeover for a while followed by the same civil uprisings as OTL, only here without Mussie some other faction becomes the dominant anti-Socialist paramilitary group, possibly Authoritarian Nationalist "Blue Shirts" or some other "Black Shirt" type group based on the fasci di combattimento. Maybe di Annunzio is at the helm, in which case expect wackiness.
In the end there's little the government can do to prevent the chaos so some group will eventually grow strong enough to demand power. They either a) lack the Fascists' political skill and just go for revolution and Italy breaks down into total civil war or b) they have the political skill and manage a Mussie-style takeover at the king's behest.
If a) Italy looks like Spain a decade earlier; perhaps the army just steps in and takes over. If b) then who the hell knows...depends on the politics and aims of the group that takes over. Could parallel Fascism or look more like Francoism or Salazarism or Naziism. Could be a standard authoritarian state. Could go more socialist or syndicalist. How they align internationally is another guess based on the regime.