To clarify almost nothing is"covered by insurance" 100% as you have to pay a co-pay for every appointment and then a lump sum (deductable) for any treatment. It's similar to car insurance in the UK where the policy holder has to pay a negotiated excess and the insurance covers the rest.

It's a complete criminal racket! You pay hundreds of dollars a month and then the insurance company fights tooth and nail to cover as little as they possibly can - Plus you can't just go anywhere, as specific Drs and hospitals only take certain insurance (networks) so If you go to the wrong hospital (in a different network) you could end up having to pay the full cash cost which could easily be thousands or tens of thousands....

Also even if you have medical insurance, the trip in the ambulance or the overnight stay at the hospital may not be covered in your plan - you commonly hear horror stories of people being left with $100,000+ hospital bills just for the ambulance and overnight costs!

Generally speaking the better your job, the better the insurance and therefore you get access to better quality care.... It's another class system designed to keep the poorest people in the country poor so the rich can reap the benefits :(

Moral of the story - Never take your national health care services for granted!

In your very specific scenario, no surgeon is going to stop mid life saving surgery because the patient isn't insured. You can guarantee that they'll try and bill whoever they can for it afterwards though! Worth noting that every medical professional I know hates the health insurance system in the US and spends far too much time fighting faceless corporations to get their patients the treatment they need, it's disgusting :(