I work from home as a PM supporting the ACA. I work for one of the "big five" in health insurance. I'm going to keep my comments as A-political as possible, I don't have any skin in the game since I have medical coverage from military retirement so I won't comment on what's "good" and/or "bad" with regards to ACA etc.
I agree with SOL and others on the boards that something will take the place of ACA should it dissolve BUT, that's not likely.
What you might find is that some states will continue to work hard to support ACA in their states while others continue to ignore it/make it a PITA. Since ACA involves states getting to decide how they will "play in this sandbox" you see various levels of support for it.
(It's convoluted but some states run their own exchanges, some run part of the exchange, some states don't touch it and everything in that state is managed by the federal govt).
States that support ACA politically etc. continue to work hard to make it valuable, others... not so much. Where you live may become more important if health insurance is a priority and the state you want to live in doesn't support it/makes it harder to enroll.
Problems with ACA. Since it's not under-written, more and more "sick folks" are signing up. That means healthy enrollees are/and will continue to subsidize the premiums of those who are not healthy/have very low income. If you can get on an under-written policy in some way, you'll likely pay less. In addition, in some states/areas, insurers are receiving "about" .35 cents on the dollar from what they were expecting in payments from the federal govt, reducing profits and making it harder to attract quality companies in those areas. So the downward spiral (less choices, less competition, higher premiums) continues in some areas, while others have robust competition, pushing down some rates.
The future? If states get the option to opt out in the future, some of them WILL. It may be that it becomes a "play if you want to" model and folks will move to obtain health insurance in another state. Also, MEWAs (google will help) are becoming more popular and may take on some of this role.
In some states there is talk of allowing ANY group large enough to negotiate with insurers the "right" to form their own health care plan/group (AKA association plan). This MIGHT mean that if enough FIRE folks got together, they could negotiate and sell their own policy to those who are part of the group. Or, everyone in a car club, in multiple states, might be able to form a Small Group plan, things of that nature. Of course, the various sides of the issue wade in and put up roadblocks/disagree with allowing such things so they are probably a LONG ways off. I could see them "jumping off" if the ACA were to totally implode.
Lastly, the big companies are working HARD to reduce internal costs and automate as much of the filing processes as possible which MAY reduce ACA premiums (or they pocket the extra profit...). If premiums come down, more folks join, the cycle grows and it is much harder to kill ACA for good.
I know, not that helpful, but maybe a few nuggets in there.