they assume TRUMP can't win the general and the damage he would do as the GOP nominee would be worse than denying him at the convention.

like I said before, Trump has brought in a lot of new voters...that have probably never voted in a GOP election. Those voters will be very pissed, but won't crater another nominee's chances. Especially against Clinton.

Rubio, Kasich, Cruz will all stay in - to split up the votes...then the real fight begins.

Trump, to run 3rd party, would have to decide WAY WAY before the convention. Like, pretty soon to get on the ballot nationally. State's have sore loser laws that could prevent it in many states. He could get another party like the consitution party to support his bid, which could be easier, but still alot of legwork and money to get the signatures.

If he was able to get on the ballot - i think he'd likely hand the election to Hillary, but it depends on who the candidate is...if it's Kasich - it would be pretty close....and there is a lot of anti-HIllary sentiment.