That's extremely rare (in fact, I couldn't find a single instance) and what drivers insurance is intended to alleviate. It would take a lack of insurance by the driver (and you, if you were driving), lack of medical insurance, a particularly expensive-to-treat injury, lack of savings and lack of community support before we get to bankruptcy.
How could you possibly know what the status of any given motor vehicle accident victim's insurance or financial state is at the point of impact? I suppose I can break it down further. What if I were walking across the street and hit by an uninsured motorist (an illegal immigrant, perhaps)? That is a catastrophic injury that could certainly result in a long-term hospital stay with potentially multiple life-saving surgeries required (head, neck, spine), plus physical therapy and likely long-term care needed to manage the aftermath. Tell me again, why is it that the act of crossing the street should ruin me physically and financially?
It (probably) shouldn't. But like I said, it's extremely rare (to the point where I'm not even sure it actually happens). And such an extreme edge case that it shouldn't debilitate the whole rest of the system.
Then disregard that example and simply substitute it for getting sick with cancer or something if it seems too far-fetched to you, it does not seem that way to me.
Regardless, medical bills are the leading cause of bankruptcy in the United States [1]. How can we live in a society where anyone but the wealthiest individuals could be struck down financially at any moment? How much entrepreneurship is completely stifled by the need to stay at a particular job due to proper healthcare coverage? I would venture to guess the answer is quite a lot.
