The election will move forward as prescribed by the date in the Constitution even if BOTH Hillary and Trump are out. The winner of enough electoral college votes even if it's right now someone pulling .001% polling, wins.

If not enough electoral college votes are determined for any one candidate, the selection of the new president goes to the votes in the House of Representatives.

1/20/2017 Obama is fired regardless. There is a Constitutional amendment to solidify there cannot be beyond a second term.