DES MOINES — (CNN) With or without Donald Trump, the show must go on.

Republican presidential candidates are set to clash Thursday night in their last debate before Monday’s Iowa caucuses.

Plans for the showdown were thrown into turmoil after Trump, the national front-runner, said he would not show up after a long-running dispute with Fox News. Still, there’s likely to be plenty of drama, both on the debate stage and at the veterans event Trump plans to attend instead.

Here are five things to watch on debate night.

1. Can Trump win a debate without showing up?

Trump is overshadowing the debate even as his campaign says he won’t show up.

He has shown, yet again, that the normal rules of politics don’t apply to him and made a statement that no one messes with Trump. And if his army of followers simply decide not to tune in, he’ll be punishing Fox by denying them the monster ratings this year’s debates have attracted.

Trump won’t be gasping for the oxygen of publicity because the media has been on a 24/7 Trump binge for months, and the lead-up to Thursday’s debate has been no exception: His promised nonappearance has been the major story line.

By staying away, Trump would avoid a new and potentially damaging engagement with Texas Sen. Ted Cruz after their showdown in the last debate as well as dodge other opponents desperate to draw him into a last-minute gaffe before Monday’s caucuses.

At the same time, anti-Trump rivals have a clear opening to claim their tough-talking nemesis is running scared. And there will be no one to defend Trump if the field decides to pile on — though experience suggests it’s just as likely his GOP rivals will anger Trump’s loyal supporters and hurt themselves.

Still, Trump is willing to pass up a final chance to convince Iowa voters currently leaning toward other candidates or even wondering whether they will show up on Monday night. With his fate in Iowa depending on turning out new voters, a no-show at the debate is definitely a risk. Iowa political activists are also highly sensitive to any perceived slight toward the caucuses, and devaluing the state’s last big debate of the cycle would certainly fit that category.

If Cruz, for example, shines — and wins on Monday night — Trump’s gambit is sure to be second-guessed.

2. Cruz in control?

If Trump is indeed a no-show, Cruz may stand alone in the crossfire.

He has been fighting a close race with Trump in Iowa and is well-positioned in a string of Southern states that go to the polls in March.

But the Texas senator does have work to do. Though Hawkeye State experts talk up his grass-roots political operation, the conventional wisdom of just a few weeks ago that Cruz was gliding toward a caucus triumph is suddenly looking different: The latest CNN “poll of polls” in the state has Trump up by 5%.

After his one-time truce with Trump buckled as the Iowa vote has approached, Cruz is now to be deprived of a chance to rough up the real estate mogul himself and shave off a few hundred votes that could be important come Monday night.

Still, his rival’s expected absence gives Cruz the chance to dominate the outsider, conservative spot in the debate on his own.

And there’s a silver lining for the Texan: With Trump elsewhere, no one is likely to hound him over whether he is eligible to be president because he was born in Canada.

3. How much ‘silliness’ will there be?

It will be odd to watch a Republican debate without seeing candidates mocked for anemic poll numbers and Jeb Bush getting bullied. Trump’s disdain for fellow candidates, particularly Bush, has been a staple of previous Republican debates. The dynamic of the evening will be much different withe the ferocious front-runner offstage.

Kentucky Sen. Rand Paul, for one, won’t miss Trump, telling CNN’s Jake Tapper on Wednesday that Trump only brought “silliness, bombast and empty rhetoric” to the previous debates.

So it’s possible that Thursday night’s debate could be a more civilized, policy-heavy affair on big questions — including tax policy, the war against ISIS and the wisdom of “boots on the ground” interventions abroad.

But several candidates may be spoiling for a fight and could toughen the tone.

New Jersey Gov. Chris Christie, for instance, had hoped to brand himself as the straight talker of the Republican presidential race but saw his opening closed off by Trump. So, he has an incentive to make some noise. There’s little love lost among the rest of the field for Cruz — and there may be a replay of a tense clash between the Texas senator and the other young potential heir of the conservative movement, Florida Sen. Marco Rubio.

Bush, a former Florida governor, already seems to be in a sour mood, warning in an interview with CNN’s Gloria Borger on Wednesday that his fellow candidates should not suddenly act tough now that Trump is gone.

“They’ve all been kind of polite and scared of him, I guess,” he said. “Now that he’s not there they might pile on, which I think will look a little weird.”

4. Who will win the debate within a debate?

Thursday’s debate will be in Iowa. But many of the candidates’ minds are already in New Hampshire. Of those on stage on Thursday, only Cruz seems to have a realistic chance of taking down Trump in the caucuses, if the polls are accurate.

So the focus of many of the rest, including Rubio, Bush, Christie and Ohio Gov. John Kasich, will be on the next contest in the Granite State the following week, which could vault one of them into the long-vacant spot of establishment alternative to Trump and put the others’ campaigns on life support.

Desperate for survival, the more conventional candidates have been waging a vicious advertising war in New Hampshire, and the high stakes could mean their internecine war spills over into live TV on Thursday night.

5. Will the candidates feel the Bern?

On Wednesday, Bernie Sanders was at the White House. On Thursday, he could find himself under a sudden GOP assault.

The suddenly famous Vermont senator has a real chance of beating Democratic front-runner Hillary Clinton in the first two nominating clashes.

So there’s a possibility that after spending months slamming Clinton over Benghazi, her emails and her integrity, the Republican candidates will at least train a little fire Sanders’ way.

While Sanders is still a long shot to win the nomination, the self-described democratic socialist’s surging campaign offers an opening for a Republican with an eye on the general election to portray the Democrats as a party way to the left of the mainstream. And whether they do so will say something about how seriously they take his chances.

The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: AP Photo/Mark J. Terrill)