Haley is the consummate pragmatist, and as long as Trump is controlling the base, she will continue to be a Trump sycophant. She doesn’t have a single opinion that isn’t based on a poll, and Trump still polls well.

He won’t show up for the debates because he doesn’t have anything to gain, and has everything to lose. If he stands up next to people making coherent arguments (I’ll disagree on the “sane” bit, but that’s not the point), then he will bolster them at his own expense. His followers won’t watch the debates if he’s not there, and the people watching don’t get to see him fumble the ball.

He also doesn’t have the time or money to prep for the debates anyway.