A couple weeks after my DH celebrated his 30th birthday he woke up to a numb arm. He thought he must have slept on it funny. It was still numb a couple days later so he went to a chiropractor, thinking he had a pinched nerve. The chiropractor aligned him but told him that the issue he was having was not related to a pinched nerve, he recommended that my DH find an neurologist.
A month and a spinal tap, MRI, several office visits, and blood test later my 30 year old healthy DH was dx'd with Multiple Sclerosis. His family has no history of MS. This was a couple years before ACA fully kicked in. Luckily he was insured through my work or those bills would have completely ruined us. If he didn't have insurance at the time of the dx'd than he would have fallen into the pre-existing illness and not have been able to get coverage, this is not an issue now because of the ACA.
His drugs for MS, without insurance or rx assistance programs would cost $5-8k a month, with insurance and the rx assistance program we have paid anywhere between $0-$50/month for his medicine. He has experienced several symptoms of MS. His attitude started to get pretty negative, so they put him on antidepressants. His sleep patterns were irregular, so he now has a C-PAP (which help him get off the antidepressants). He gets an MRI every 2-3 years, blood tests every 6 months, and sees a neurologist every 6-12 months. He is still working and active (no disabilities) and without insurance it would take less than 10 years for his medical treatment to reach $1M.
MS is not fatal and it is said that people with MS can experience a normal lifespan. Life expectancy for people with MS has increased over time. Some believe this is due to treatment breakthroughs, improved healthcare and life style changes. This is important to your point that one would probably not make it through $1-2M in medical cost. The average age to be dx'd with MS is 30, if my DH lives to the average life expectancy of 76 years old he will have lived with (and been treating) MS for 46 years. If it takes approximately 10 years (without insurance) to reach $1M in medical care we would need to be prepared to pay $4.5M in medical care for him (without insurance).
Stay insured, you never know what might happen tomorrow.