If you don't have insurance in Germany you'll have to pay for that yourself as well. That's rare, but it happens especially with the precariously self-employed.
The issue with the US system is that you can't have it be both non-compulsory but also that coverage must be offered to everyone, no matter their state of health. Then you'll have a few healthy people pay huge premiums to finance treatment for those who never bought insurance until they're sick.
It is my understanding that a compulsory purchase (as in Switzerland) would be unconstitutional, so I guess "Medicare for all" in the form of a tax would actually be the next best thing. Just keep in mind that with US levels of healthcare salaries, that wouldn't come cheap.