Would it be unreasonable to hold another vote in such circumstances? With such large numbers voting, close outcomes like this have got to be a rare event, so it seems practical enough to hold the occasional second ballot.
How close would it have to be in order for us to declare it to close to call? Even if some number could be stablished, say 100 votes for instance, what would we do if an election came down to 99 votes (or 101)? would we declare it to close to call wheather it is to close to call? As you can see, introducing a third possible outcome for an election - to close to call - between the two traditional ones - A wins, or B wins - does not preclude the need to make a decision and therefore doesn't really solve the problem. Might as well leave things the way they are.