Exactly how things work in different areas of the country, or even in different hospitals in the same area or region, can vary greatly. I can only speak for what I've seen and experienced. I know where I work there is a certain percentage of the budget is put aside for care for the uninsured. The hospital does eat some costs. (And the rest is probably complex, like perhaps there are tax write offs or something, not really sure.) And I've also read in various places that if people have large bills, they may be able to negotiate what's owed, or at the very least, set up a payment plan.
But I do believe that in most hospitals, people have to sign that waiver during the official admission process. It even happens now in doctor's offices when you sign in - you have to attest that if your insurance won't pay for services, that you'll be responsible for it.
Just to add to the discussion, a lot of people blame hospitals for a lot of the high costs of care, and I'm sure there's some truth to that. But everyone wants the best treatment and the best care with the least amount of aggravation, etc. I think many hospitals try to do that for people, but it isn't cheap to provide that. Hospitals know that if they don't pony up, people will go elsewhere, so as businesses, hospitals have to figure out a balance between surviving, staying profitable, and giving patients what they want. Very complex today, and no easy answers to solve the problems.
I will say that patients getting admitted to hospitals today often have complex medical needs, and hospitals are expected to perform to a certain high standard. With the onset of the ACA, Medicare (the government run insurance program for people over age 65 who paid into the system) started implementing very large fines for standards that were not met. Some of these fines are extremely high, like $30K per incident, per patient, say if someone develops a urinary tract infection from a urine catheter (who doesn't?) or a pressure ulcer/bed sore, or if they are readmitted to the hospital within 30 days for certain things, etc. This has been a huge strain on hospitals, because as you can imagine, problems do come up when care is very complex and someone, say, is unconscious for a week or otherwise very sick or debilitated. But very few are talking about that. In addition to fines, for many years, Medicare has lowered reimbursement rates to hospitals for many things, and elderly insured by Medicare comprise a large portion of patient populations, so more and, in essence, better care is being given, yet reimbursements to hospitals are lower and fines are larger and more prevalent.
https://khn.org/news/more-than-half-of-hospitals-to-be-penalized-for-excess-readmissions/
http://www.sandiegouniontribune.com...cquired-penalty-medicare-2015dec26-story.html
https://www.beckershospitalreview.c...o-know-about-medicare-reimbursement-2017.html
So bottom line, these are challenging times for hospitals, too.