Early in the pandemic, Mr. Klimavicius, like many, had his doubts — theater was dark, Midtown was dead, everything seemed uncertain. But this June, buoyed by $4.5 million from the federal government’s Restaurant Revitalization Fund, he began overhauling the space — redoing the kitchen, the gas lines, the ventilation, and the wiring, among other things — hoping to modernize it in a way that no one would notice. People who love Sardi’s are, to put it mildly, change-averse.

“I was concerned when I heard ‘renovation’,” said Andrea Ezagui, a Sardi’s regular from Long Island, who showed up at 4 p.m. — the moment it reopened — and immediately repaired to the bar upstairs, where she celebrated with champagne and friends. “They kept it the way it should be,” she said, “a little piece of heaven on Broadway.”

The restaurant’s famous caricatures came off their picture ledges for the restoration — all but one, that is. Barbra Streisand has the only caricature screwed to the wall, because fans stole the original; so now she remains, irremovable, with her admonition “Don’t steal this one” inscribed above her signature.

On a recent afternoon, Mr. Klimavicius and his crew set about putting the hundreds of caricatures back up, starting with one of Lin-Manuel Miranda, “a good friend of the house.”

As he settled into his domain on the second floor, Mr. Petrsoric, the bartender, was clearly relieved to be back on the job, after spending too many months in Mamaroneck, N.Y., riding a stationary bike and, by his own account, going crazy. “What am I going to do at home?” he said. “I love people. And think about 50 years behind the bar. You know how many people I know?”

He started by mixing a Belvedere martini, a cosmopolitan and a lemon drop. “This is unbelievable,” he marveled. “But you know, it takes me one hour, and you’re back to normal.”