This sounds like a spin off to the "Our Struggle" TL
Realistically he probably gets killed or exiled from Italy.
If Benito was able to lead a socialist revolution it would get quite bloody when they went head to head with the Vatican.
Maybe the Vatican ends up an earlier equivalent of West Berlin surrounded by a communist state?
WIth the USSR and Italy going communist perhaps the rest of the dominoes fall in Europe, Hungary, France, Germany, etc.