What might result if individuals failed to fulfill their duties as citizens?

If it's a country that claims to be a democracy, that democracy would fail. A democracy depends on citizen involvement-- especially voting, but also running for office or supporting candidates and causes. It also depends on a free press and the oversight of journalists, to keep the government honest. If no citizens participate, if there are no impartial and involved journalists, that could enable the emergence of a Dictatorship of some kind.