No. Not for a leader.
He may have been atheist at some point in his life but it’s clear he didn’t remain one.
Why do you say that? Who died alongside Mussolini in April 1945?
It’s clear Mussolini did not remain atheist because of records indicating threat of excommunication following the Lateran Pact and the concordat that followed.
One cannot be excommunicated from a church to which one is not acknowledged to belong.