Actually, things might be far more problematic for Mussolini than the scenarios already described would suggest. Unlike most conservative autocracies, the Fascist revolution was conceived by its intellectual supporters and by the Italian populace (though in a more subconscious sense) as an epic project to create a new world order, a system of belief where the complexities and hypocrisies of the modern world would be simplified and erased, and a new national community would be formed. Unfortunately, as events in Germany, the Soviet Union, China, Cambodia, Japan, and so many other nations have proved, forging national myths is not a task that can be directed on high. By the middle of the 1930s, even before Hitler’s influence came to dominate the political landscape, Fascist Italy was beset by any number of familiar problems, namely national apathy among the general populace, a party apparatus that was congealing into a bureaucratic gerontocracy, an exhausted autocrat in command with no successor, diminishing returns on industrial and imperial megaprojects, and a growing alienation by the intellectual supporters of the regime, many of whom moved into the anti-Fascist resistance during the war. While I’m not saying that Italy would collapse by 1945 even without a Second World War, I would say that the system was not suited for the rigors of ordinary governance (Say what you will about the communists, but at least they knew how to run a bureaucracy). I’d recommend Simon Louvish’s The Resurrections for a worm’s eye view of the death of Mussolini in 1968, and the utter free-for-all that emerges in his death.
In this case, I doubt history would judge Mussolini kindly. Still, his final image may be that of a sick old man, out of touch with the world he once commanded, rather than the clownish image we have today. I can’t really imagine the world at large viewing him with any malice, unless some new regime came to power that made anti-fascism a fundamental part of its claim to legitimacy.