There are a few independent (neither democrat or republican) candidates who could win a few electoral votes. I think that is highly unlikely at this point.
You are correct that with a binary-choice it is nearly impossible for one candidate not to win. Each state has a certain number of electoral voters given to it based on population. Usually the winner of the state gets those electoral votes. However, there have been cases in our history where the electoral voter votes for someone else.
The system was set up to be a check and balance type system. It is rare to have the electoral votes not echo the voice of the people in the state, but it can happen.
Just in case a candidate does not receive the 270 or more electoral votes needed, the House of Representatives decides who will be the next President. That has not happened in my lifetime and I can see that being a total mess today if it happened. But it has happened in our history.
Steem on,
Mike