There's a moral question at the heart of this, the answer to which defines the solution space: do we, as a society, think it is important that all sick people receive care? If yes, there are a bunch of potential solutions, but they all involve healthy people subsidizing care for sick people. If no, there are, of course, a lot more options.
The thing that frustrates me about the current Republican approach is that they seem to want to answer "yes" to this question, while telling voters they will not have to subsidize care for the sick in any way.
Depending on your point of view, either the best feature, or the biggest failure, of the ACA was that it made this subsidy for the sick visible to anybody buying their own insurance, rather than hiding it behind taxes or complicated dynamics between governments, insurers, employers, and hospitals.
A little more succinctly: either we decide to let emergency rooms turn sick people away, or somebody will be paying for their care. There's no magical solution.