The biggest crisis in health insurance isn't going to be the withdrawal of ACA. It's going to be the destruction of the CDC and hundreds - if not thousands of public health programs that quietly monitor/screen and coordinate responses to possible outbreaks. Vaccination programs have gone, and no employee or educational facility can require employees or students to be vaccinated or asked to mask.
Insurance premiums are largely calculated by risk. Diseases that were once regarded as eradicated are already making a comeback.
And since the risk is exponential, the calculations are far higher than you might imagine. On average, one person with measles transmits it to 12-18 people. Untreated TB, 10-15 people. Measles is contagious from 4 days after catching it - symptoms appear 7-21 days after contracting it. Insurance companies must budget for worst case scenarios - and are happy to.
Meanwhile, hospitals are forced (to an extent) to offer care to people who can not, or will not pay. They will try to recover their costs by raising prices on other services, and insurance companies will feel that too.
The GOP is doing for heath insurance, what climate change has done to home insurance in Florida.