If a State fails to send electors, then it fails to vote in the Electoral College—which it can Constitutionally choose to do (not vote.) But if a State does not vote, then the number of votes required to win is reduced, because the Constitutional winner is whoever gets the most Electoral votes out of those actually cast.
The language of the National Archives supports your statement.
“If no candidate receives a majority of Electoral votes, the House of Representatives elects the President from the 3 Presidential candidates who received the most Electoral votes. Each state delegation has one vote.”
If the House were to not elect Donald Trump, I don’t want to think what would happen.