SANIBEL, Fla. — Nightfall was near and three men in the rescue crew were hustling back to their boat when Lisa Stasi, her voice strained with worry and exhaustion, flagged them down from her balcony on Sanibel Island, Fla. Hurricane Ian had turned her neighborhood into a disorienting landscape of wreckage.

“Can we go?” she called out. “What do we have to do?”

“Pack a bag,” said Bryan Stern, the crew’s leader, from her sodden driveway.

Turning inside her home, Ms. Stasi yelled at her husband: “Beaver, we’re going!”

James Judge, the rescue crew’s boat captain, looked up at the dying sunlight. They would have to hurry; the island would soon be pitch black. So would the bay they had to traverse to reach the mainland. They would risk crashing into an overturned vessel or other unseen storm debris in the dark water.

For three days, Mr. Stern and his team had been making trips to Sanibel, North Captiva Island and St. James City, barrier island communities that dot the southwestern Florida coast along the Gulf of Mexico and bore much of the brunt of Hurricane Ian’s ferocious winds and turbulent storm surge. Cut off from family, friends and supplies by Sanibel Causeway’s partial collapse, the islands’ residents who had stayed and survived were stranded. About 200 households on Sanibel, which has a year-round population of about 6,500, had not evacuated despite mandatory orders.

Lee County, home to Sanibel and the battered cities of Fort Myers Beach and Fort Myers, has confirmed at least 42 deaths after the storm. Between 600 and 700 people have been rescued, Sheriff Carmine Marceno said on Saturday, adding, “We’re out in full force.”

Loved ones frantically phoned local fire departments and rescue organizations during and after the storm to report their relatives’ last known whereabouts. One of the groups recording names and addresses was Project Dynamo, the nonprofit that Mr. Stern, a U.S. Army and Navy combat veteran, founded 13 months ago to help rescue Americans from Afghanistan and later Ukraine. Mr. Stern lives in Tampa and was home from Ukraine on vacation when Ian bore down. He stayed — and then found himself activating his volunteer network for rescues unexpectedly close to home.

“Pure hell,” Mr. Stern said to describe the days since Ian made landfall in Florida on Wednesday.

There was the older man who used a wheelchair. The amputee. The older couple with mobility issues who were unable to get into the rescue boat, so the Project Dynamo team called for a Coast Guard helicopter, one of several that buzzed incessantly overhead as they conducted rescue after rescue.

The gulf side of Sanibel was ravaged, Mr. Stern and Mr. Judge said, describing homes ripped off their concrete slabs. Some boats had landed on the roofs of houses. The bay side had fared better: Stately elevated homes still stood, many with torn roofs that exposed dining tables and living rooms. Thickets of snapped trees piled up everywhere. House alarms blared. The air smelled of mold and mildew.

Sanibel had been a slice of paradise for those who could afford it. Lush and beautiful, it was a charming beach town with golf courses, canals and street names like Sand Castle Road and Periwinkle Way. The median annual household income is more than $92,000. The island was like a living postcard for coastal Florida, appealing to mainlanders jaunting over the causeway for a quick visit, seasonal tourists and snowbirds.

“It’s wild driving by and seeing places where we were having a burger two weeks ago, and they’re gone,” Mr. Judge said. “It’s just nuts.”

On this run in his 29-foot central console boat, Slice of Life, the Project Dynamo team was looking for a pregnant woman who had ridden out the storm on Sanibel with her parents. It tied the boat to an open dock, clambered over the muddy shore and reached a cratered main road. Without a GPS unit or a paper map, the team tried to figure out its way around using an offline map on the cellphone of the third crew member, Scott, who declined to give his last name. Like Mr. Stern, the teammates also have military backgrounds; Mr. Judge was in the Coast Guard and Scott was a drill sergeant.

They walked in a row under the hot afternoon sun. Someone from the fire department gave them a ride in a pickup truck to reach the pregnant woman’s house.

“Jennifer!” they called out. “Jennifer!”

“She’s already gone!” a man yelled back.

It was Jennifer’s father, Buddy Long. His daughter had hitched a ride out earlier on Friday. Mr. Long and his wife, Pam, were still home, drying out clothes and towels on their front railing. The crew offered to take them out.

“I think we’re going to be leaving in a day or two,” he said. “We’ve got soup. We’ve got a camp stove.”

“Well, your bridge is completely gone,” Scott said. “You won’t be back for a while when you leave.”

“I figure it’s probably going to be weeks,” Mr. Long replied.

“I think months,” Mr. Stern said. The Longs stayed.

Mr. Stern peered at his rescue list. His wife, Olivia, a Pilates instructor who works the phones for Project Dynamo to help manage the group’s cases, had written out names and addresses on paper. Mr. Stern had placed it in a Ziploc. A guy on a bicycle drinking a can of hard seltzer rode by.

“He deserves it,” Mr. Judge, who is running for Congress as a Republican, said with a chuckle. “Definitely deserves it.”

To reach the next house, the team crossed a golf course, parts of which looked more like lakes. The rest was covered with dead fish from the storm surge.

Betty Reynolds, 72, sat on a white bench outside her front door. At her feet were four garbage bags and a tote. She seemed to have been expecting them.

But she was not. And she had no intention of going, at least not yet.

“If you don’t go today, it’s unknown when it’s going to be,” Mr. Stern told her.

But Ms. Reynolds, whose first floor had reached more than waist-high with mucky surge waters, said that she had not packed. She had not changed her clothes. And she had supplies to last two weeks, she said.

“The upstairs is really fine,” she said. “The cat and I do really well there.”

The crew emphasized the dangers posed — especially to older people — by the heat and, in her case, the warping and slick floors. She admitted she had fallen as Hurricane Ian roared through.

“It took me about 30 minutes to maneuver myself,” she said. “I just said, ‘I’m not going to drown in the kitchen floor.’”

Ms. Reynolds had evacuated for hurricanes before. But now she had two solar-powered generators and figured the worst of the storm would be its winds. Neither she nor her neighbors counted on the surge. Now she had no power, not even from the generators, and no running water. Her daughter in Washington had called the rescue team, worried about her.

“You all are making a very convincing argument,” said Ms. Reynolds, who is from Arkansas. “But this is 47 years of my life. This is not my vacation home. It’s where I raised my children.”

The crew trudged back to the boat. It appeared they would leave with no passengers. Then Ms. Stasi, 65 and originally from New Jersey, waved from her balcony asking for a ride.

“My husband doesn’t want to because he’s going to barbecue,” she said.

But her husband, Beaver Stasi, 66, did come. So did their 34-year-old daughter, Courtney Stasi, and her cat, Boo.

“You have IDs?” Mr. Stern reminded them. “Jewelry? Important documents?” (They did.)

Roller suitcases in hand, they headed down the road. The fire department had promised to come for them in the afternoon but had not. They had evacuated for Hurricane Irma in 2017 but thought Ian would not be as bad.

“My house, I could feel it moving,” Ms. Stasi said. “We should have left.”

Mr. Stasi, in flip flops, moved slowly. He had fallen down the steps on Thursday and cut his arm.

“No electricity. No air-conditioner. Very limited food,” he said. “But other than that, we were together.”

Lyndon Borror and Elizabeth Boone, their neighbors, joined the walk to hear about how the storm had impacted other parts of the county. Ms. Boone had little hope that her house on South Fort Myers Beach had survived.

The sun set and the eerie night fell. The rescuers held tight under Mr. Stasi’s arms to walk him over the road crater. On shore, the family would be met by a paramedic and volunteers to help find them a place to stay.

The Stasis boarded the Slice of Life in the darkness. Mr. Judge got the motor running and offered them bottles of water. From up the road, their neighbors bid them farewell with the twinkle of a flashlight.

Audra D. S. Burch contributed reporting.