Actors have traditionally lived by the mantra “the show must go on,” but these days, of course, big stars have to know the script’s right, the money’s good and the co-stars are suitable.

You may have heard that Jennifer Lopez recently dropped out of the film remake of the TV soap “Dallas.” She was supposed to play Sue Ellen Ewing (originally played by Linda Gray), opposite John Travolta’s J.R. Ewing.

Speculation that a poor script, combined with possible displeasure at the choice of leading man, has been bandied about in the press.

One thing’s clear to me: Travolta doesn’t seem too broken up over J-Lo’s departure.

I sidled up to him at a recent 80th birthday dinner for Tony Bennett in New York and asked him about it.

He flashed a killer smile and said, “We’ll get someone who’s more excited about the idea. It’s not going to stop us.”

Few actors other than Travolta can swing the pendulum on film like he can — he’ll go from macho J.R. to big momma Edna Turnblad in the film remake of John Waters’ “Hairspray,” the role originated by drag queen Divine.

Also at the Tony Bennett event was former New York Gov. Mario Cuomo, a Queens, N.Y., native like Bennett.

I asked him how he would handle the Middle East situation if he were in office, and he gave a very sobering (and frightening) response.

“The reality is unless the whole Middle East accepts the idea that Israel is a legitimate nation, you’re gonna have these wars until somebody goes crazy and drops an atom bomb and then we’re all gone.”

Wow — uh, check please!

Here’s Cuomo on Bennett reaching 80: “He’s still as simple as a loaf of bread.”

Bennett talked world events, too, but with a bit more optimism.

“I don’t believe in violence. I believe in peace. No matter how many people say there will always be wars … I wasn’t raised that way. I believe someday it’s going to stop. Cause it’s the lowest form of human behavior.”

Two of the Dixie Chicks — sisters Emily Robison and Marti Maguire — were supposed to be at Bennett’s party, but didn’t show. I wanted to know how he felt about entertainers speaking out about politics.

“If it’s honest and it’s truthful, it’s good. I like the truth. I’m against people being condemned for speaking their mind.”

Still, he says it “hits me funny. When I started out, entertainers were entertainers, and politicians were politicians. Now entertainers are politicians, and politicians are entertainers. It’s like a new planet. I feel like Rip Van Winkle.”

Also toasting Tony was Katie Couric, who says she met him “probably 10 or 15 years ago on the 'Today' show."

They’ve had some interesting times together, including shooting a GE corporate video for former CEO Jack Welch, and Bennett’s serenade on Couric’s last day at the “Today” show.

She also has his paintings hanging in her house, as Bennett is an avid artist who just had a piece accepted into the Smithsonian Institute.

After talking Tony, she filled me in on the feedback she received from Americans on her recent “listening tour,” paving the way for her new "CBS Evening News" post.

“Many people say they want a little more perspective on stories,” said Couric. “By the time the evening news is on they already know the headlines of the day. I think people really want a sense of, ‘What does this mean to me? What are the ramifications of this event? Are there any solutions?’ So I think they want us to go a little deeper. And of course that’s challenging in an evening newscast.”

Enjoy the summer, Katie. Your September debut is just around the corner.