We'll see. I think it's too early to know how that will play out. I don't think it's in the RNC's interest to put all its eggs in Trump's basket. (The RNC has to "manage" Trump the way someone needs to "manage" your most difficult relative at Thanksgiving, so he doesn't ruin everything... but privately I doubt they're very keen, or positive about his general election chances, at this point.)

For better or (mostly) worse, lots of folks run for president mainly to raise their profile—to sell a book, angle for a TV gig, or build name recognition for future races. Those candidates will NOT pass up their opportunity for nationally televised debates. I'm willing to bet they'll happen, even if Trump won't take part (which I have my doubts about anyway). And if Trump's not there, I'm pretty sure Christie will just pummel him in absentia.