That ending was altered in the 1955 animated version, which removed the humans, leaving only the nasty pigs. Another example of Hollywood butchering great literature? Yes, but in this case the film's secret producer was the Central Intelligence Agency.
Later, the CIA bought the rights to Animal House, thinking that it was going to be a remake of Animal Farm. The project was abandoned and sold off soon after they found out it had nothing to do with Orwell's novel, but not before they tinkered with some possible rewrites. In the CIA version, the Omega House triumphs over the Deltas , saves Dean Wormer and the Faber College Homecoming Parade.
Dean Wormer with future White House aide and CIA Director, Gregg Marmalar.