I think it’s reasonable to talk about what would have happen if Congress repeals the Affordable Care Act without replacing it because there is no assurance that anything will replace it. The Republicans can try to reassure people that all these horrible things won’t happen, but there’s no reason to believe they’ll be able to make good on that promise.
For one thing, the reason that horrible things will happen is because they want to get rid of most of the things that make the health care scheme work. In order to make it possible to be profitable while insuring people with pre-existing conditions, you need lots and lots of healthy people paying premiums who don’t actually use much health care. That’s why there is an individual mandate. The subsidies in the individual market and the Medicaid spending are what makes it affordable for millions of people to get coverage, so if you eliminate or drastically reduce those subsidies, tens of millions will lose their health care access. The Republicans’ plan is not fully developed, but we know that they things they don’t like are the things that keep the insurance pool of young and healthy enough that premiums can be kept at an affordable level.
What the GOP is going to attempt to do would be unpopular even if they had better intentions for many of the same reasons that Obamacare has struggled to maintain widespread support. People will be forced to change plans and doctors. Insurance companies will stop serving their market. They’ll get blamed for premium hikes even if, somehow, those hikes are lower than they have been in the past.
To avoid some of this, they’ll need to avoid messing up the scheme, but they can’t do that if they break the scheme apart.
Most importantly, they’ve arranged things so that they need only fifty votes in the Senate to mess things up but still need sixty (and a majority in the House) to fix them. Republicans won’t want to replace what they’ve just repealed, especially the things they hate. So, it looks like an impossible task to replace Obamacare with anything that would work.
Needless to say, they won’t be able or even willing to keep Trump’s promise to provide everyone with health care even if they can’t afford it.
What will they actually do?
I’m not sure that anyone really knows.