Electors don’t vote as a bloc, but should it go to the House, state delegations vote as a bloc; one vote per state. The Senate votes for VP from top two candidates, one vote per senator.
Congress can accept or reject single electors or whole state electoral votes as they see fit.
Should they deny Trump, why would Congress pick Hillary or Kaine when they could have Pence or Paul Ryan?
I don’t think they would vote for Hillary, they would vote for an alternative. Ryan, Pence, Mittens whatever. If they did, it’s just as bad as Hillary. All of these people would and did get slaughtered by Trump in the primaries, there was no one wanted more than Trump in the Republican primaries. Period. The house Republicans, until proven otherwise (by supporting Trump), are just the same as the Democrats. Without Trump forcing things the way he is the country would have already been handed over to the globalist.