This news scares Fern Warnat, 59. She has gotten insurance on the federal marketplace a couple of times in the last few years. When she and her husband moved from New York to Boca Raton, Fla., she bought a policy for a few months to tide her over until she got coverage from a new job. A year later, she needed to buy insurance again when she found herself unemployed. The policy was expensive — around $800 a month.

“It wasn’t easy, but it was available,” she said.

Now she worries what would happen under the Republican plan if she left her job at a home health company that provides insurance.

“I need something to be there,” she said. “I’m going to be 60 years old. All my conditions pre-exist.”

Since the Affordable Care Act was enacted, companies have become less worried about people who want to leave but feel locked into their jobs because of health insurance, said Julie Stone, who works with corporations at Willis Towers Watson, a benefits consultant. The law “removed one of the barriers to leaving your job,” she said.

Fewer employers now offer health insurance for their retirees, she said. The other alternative is Cobra, the federal law that requires companies to allow workers to remain on their employer’s plan if they pay the full monthly premiums, which are often extremely expensive and out of reach for many people. The coverage generally lasts no more than a year and a half. Cobra was a “Band-Aid on a broken market,” Ms. Stone said.