Last week, President-elect Donald J. Trump called Obamacare “a complete and total disaster,” and pushed for a swift repeal of the Affordable Care Act and a replacement within weeks. But at the moment, there is no workable replacement. So what happens to the individual insurance market — whose problems did not start with the Affordable Care Act and will not be easily solved — when it is destabilized so dramatically?

From my point of view as a former health insurance company chief executive, “total disaster” would also describe any Republican repeal-and-delay plan. Although my former colleagues in the insurance industry are too cowed by the president-elect to say so, Republican insistence on repeal without having a meaningful replacement at the same time will drive most insurers out of the individual market and leave the 10 percent of Americans now covered by some aspect of the A.C.A. without coverage — especially if Medicaid expansion is rolled back as well.

The proportion of uninsured Americans, which has dropped to less than 9 percent, the lowest on record, will at least double. By April, when filings from insurance company plans and premiums for 2018 are due, there will be a sizable exit — of insurers running away from the greatly increased and unpredictable risk and of individuals not able to afford insurance without the subsidies.

Of course, the A.C.A. has a number of flaws, and repair is critical. But delay is not an option if the replacers really want to use private insurers to meet society’s goals of access, affordability and quality in health care. All known Republican alternatives envision heavy reliance on the same insurers that are now ready to bolt and leave a total mess rather than a defective but repairable market.