Unlikely hypothetical questions can also be on topic, even if they are almost sure not to happen, because they can help elucidate the principles behind a subject area.
Also, there is no harm in someone answering an answerable question, and there is no harm in a question not being answered if no one is bothered to do so.
In general, there should be a strong presumption against closing a question unless there is clearly no other good alternative.
Also, strange things do happen. While it may be unlikely that no one votes in a national election for Congress, if one of the offices contested in an election is a special district bond issue, or a race for city council in a city with a population of 23, or a school board race in hamlet with a one room school, the question can and does come up. Indeed, one of the criteria that Colorado law used to determine when a local government charter should be revoked is that it has had multiple general elections in which no one voted. Several local governments every election cycle cease to be as a result of that law.