Animals live without God in their equation or taken into consideration. They live merely to survive, propagate, and follow instinct. If you see life as just eating, drinking, being merry, for the day, and having no accountability as animals, then you can live like one; be my guest but you will be judged for it. They have no motive to ethics, no hell to shun, no rewards to anticipate, no Maker to worship, no Lord to obey. They are driven by survival instincts and mainly just seek pleasure and avoid pain. It looks like life without God in the metric is a bleak outlook, even a curse, and certainly not fulfilling enjoyable in the abstract.
But they have no dignity and worst of all, no rights for they cannot be in God’s image from which rights were originally derived. Animals have no deeper purpose than living for the present because they have no sense of eternity without God and live for the day. They cannot live for anything larger than themselves but are wholly selfish and not altruistic or noble with no possible virtue. They have no reason to pass on knowledge to the next generation because they don't care about that because they are incapable of planning or foresight.
I’m not saying we would be lowered completely to the level of an animal or barbarian, but we would have a lot in common with them without any religion to civilize us for man is by nature a religious creature and if he doesn't worship God, will find something or someone else to worship—perhaps celebrities, politicians, athletes, musicians, or businessmen or perhaps the rewards and aim of fame, power, and fortune.
Let me sum it up by a quote from Bertrand Russell, atheist philosopher: “Without God the question of life’s purpose is meaningless.” Soli Deo Gloria!