Well, it's not impossible. If neither candidate gets 270 electoral votes next monday, and if the House doesn't automatically flip the resulting contingent election to Trump, then balloting would continue in the House until one of the top three vote-getters earns a 26-vote majority of the statewide contingents in the House. This was supposed to be the path to the presidency for whatshisname in Utah. It is still desperately unlikely, however, as the electors are already receiving rather serious death threats from Trump supporters.
(Yes, contingent elections in the House are apparently very odd--counted by state, not representative. IANACL.)