This quote, "Suppose they gave an election and nobody came?" is the essence of what should never happen in a democracy. Elections are the way the people choose who will represent them; therefore, if an election was held yet no one came, there would be no representative elected. The people would have chosen to have no voice at all in what happens in their society which is the opposite of what should happen. That is why, when elections are held, there is almost always a tally of what percent of the voters actually voted. Voting in an election is the one thing which keeps a democracy representing the people; choosing not to vote would mean apathy or indifference as to how the government chooses to govern.
I don't know how the constitution handles this, but I would think that if no one voted, no one would be voted into office and those that are holding office would be responsible to step down, as they were not elected.
I would surmise the practical implications would be that another vote would be held and those that ran would probably run again (which is highly unlikely) or another set of candidates will rise in their steed.