Can state laws protect those with pre-existing conditions from being denied health insurance, should ACA be eliminated?  ?

Most states don't have laws like that.

In California, before the ACA, a person with preexisting conditions often had to pay over $2000 a month for health insurance.  You could buy a new car every year for that kind of money.

The biggest issue is the cost of health care regardless of how it is paid for. It is an end-to-end system of excessive money and overhead totally about $4 trillion a year or about 18% of GDP. 

https://www.businessinsider.com/personal-finance/c...

It's also full of unnecessary tests and medical fraud. Pre-existing condition issue is only one piece. Every major country has universal health care, and ACA is the USA's. There would need to be allocation of expensive services. This pandemic has killed 1 in 1000 black people, and part of that issue is insufficient health care access in general. Profiteering, costs to become a doctor, administrative overhead, marketing of medicines, fraud and bill padding, malpractice awards, excessive certifications of primary care, and more.Equal coverage of pre-existing conditions just spreads those costs around differently.

Median household income in the USA is about $60K.

At 3/household and $10K per person in cost, if a family pays all their own it takes half their money by this simple calc, even if not accurate, it's still a large chunk.

Most states don't have laws like that.

In California, before the ACA, a person with preexisting conditions often had to pay over $2000 a month for health insurance.  You could buy a new car every year for that kind of money.