Pius VIII is elected pope. Pius VIII will have to struggle with declining Church power and growing social problems, not unlike many popes before and after. Pope Pius VIII will become certain that the cause of all his problems are partly due to Catholic indifference, partly due to increased Protestant missionary work, and partly due to a conspiracy of groups like Freemasons.
For this reason, Pope Pius VIII will work hard to fight all three in the hope that he will be able to restore both social order and papal authority over Christendom. He doesn't have much time to do so, though - less than two years, and from the time he is elected he will be in poor health until his death.