Part of what makes that whole thing weird is that in order to take part in the debate, they had to sign a statement saying that they would support the eventual GOP candidate. That's why Trump wasn't allowed to participate: he wants to option to go rogue if he doesn't get the nomination. Typically, though, I'd expect him to just lie if he wanted to go that route.
For everyone at the debate, though, if they said that they wouldn't support Trump as the nominee, they would be going against the word of the document they just signed. Definitely a lose-lose situation for them. (Though they are the ones who created the Trump problem in the first place, so it serves them right)