Unless you have hundreds of millions or at least high 10's of millions, you're going to need some medical insurance.
I had a pulmonary embolism five years ago. Fortunately I was actually walking into the hospital with my wife for a procedure when it happened. I collapsed and my heart stopped - good thing I was in the hospital already about 200 yards from the ER. I was in the ICU for 10 days, a step down unit for 4 days. 4 weeks later, I had a heart attack at 3am while recovering back at home. Back into the hospital for another 4 day stay. Between that and all of the followups, procedures to remove filters from my veins, physical therapy and the like - the hospital billed me over $1,000,000 (that was for a 3 month period, another $400,000 the first six months of the next year).
Insurance knocked the $1,000,000 in billing down to the mid 400's. I would have had to negotiate that stuff myself if I self insured.
My out of pocket for the experience was under a few thousand - my max out of pocket was pretty low (I had good employer provided health care from my wife's plan - I had retired just six weeks before this all happened).
That literally would have wiped out a very sizable chunk of our retirement.
We are not relying on SS - we didn't use it when running the numbers. But I'll be taking it as will my wife. Why leave money on the table?
Medicare - when I qualify for it in 10 years (maybe they'll lower the age, that'll be nice) and 12 years for my wife will be significantly less than we pay on the open market right now. We did budget for paying for health insurance out of pocket.
so - i think unless you are incredibly rich, like hundreds of millions or high 10's of millions at least - health insurance is going to be something you are going to have to have.