I assume that "complete return" means that from the beginning,
when the animals (led by Old Major) become aware of their
human oppression and seek to overthrow it. They are
successful, and the animals adopt their "seven commandments," the
most arguably important are the first, "Whatever goes upon two legs
is an enemy" and the last, "All animals are equal."
As the novel progressess, all seven of the commandments are
chipped away until even the last one has been amended to "All
animals are equal, but some are more equal than others." The
final blow that signals the return to oppressive living comes when,
through the window, the "lesser" animals observe the pigs through
the farmhouse windows and they can no longer tell the difference
between these oppressors and their former human ones.