If the oral arguments are to be judged by (and that's definitely not always the case!) the Affordable Care Act (ACA) is not in danger of being wholly destroyed by this U.S. Supreme Court, even if Sen. Mitch McConnell and Donald Trump tried to engineer it to do that. Two conservatives—Chief Justice John Roberts and Justice Brett Kavanaugh—were sufficiently skeptical of the Trump administration and Republican state arguments to suggest they'll vote with the court's three liberals to uphold the law.
The court very well could strike down the individual mandate—the provision of the law the case hinges on—but that wouldn't make much difference to the rest of the law. With the penalty for the mandate zeroed out by the 2017 tax bill, it's now there not doing much of anything, but clearly to at least most of the justices, it's not doing any harm. The fact that Congress ended it without actually repealing the law is the key—that means it is, in legislative terms, "severable" from the rest of the law. Overturning the entire law because of this now meaningless provision seems too far for Roberts and Kavanaugh.
"I think it's hard for you to argue that Congress intended the entire act to fall if the mandate were struck down when the same Congress that lowered the penalty to zero did not even try to repeal the rest of the act," Roberts told Kyle D. Hawkins, the Texas solicitor general taking the lead for the states. "I think, frankly, that they wanted the court to do that. But that's not our job." Here's the "balls and strikes" Roberts again, refusing to be the partisan activist this time.
Kavanaugh likewise told Donald B. Verrilli Jr., the lawyer for the House of Representatives defending the law, "I tend to agree with you this is a very straightforward case for severability under our precedents, meaning that we would excise the mandate and leave the rest of the act in place." Verrilli knew the ground upon which he stood—he defended the law in 2012 as solicitor general for the Obama administration. Verrilli argued that it was too far-fetched to believe that in zeroing out the mandate penalty, Congress thought it was repealing the whole law. "There were efforts to repeal the entire ACA," Verrilli said. "Those efforts failed." So the Republican Congress did what it could do, and is chipping away with this one repeal.
Roberts seized on that, saying that removing the penalty while leaving the rest of the law in place was pretty clearly on purpose. "It's hard for you to argue that Congress intended the entire act to fall if the mandate were struck down," he told Hawkins, "when the same Congress that lowered the penalty to zero did not even try to repeal the rest of the act." To be fair, they had tried, failed, and totally abandoned the effort. Hawkins tried to argue in an exchange with Kavanaugh that Congress didn't actually intend to keep protections for people with preexisting conditions in place by not repealing them in 2017, saying that the court shouldn't actually look at congressional intent but at what the code said. The problem Hawkins has there is that the touchstone in deciding that, and pretty much any other statutory question, is "what did Congress intend."
Veteran court watcher for The New York Times Adam Liptak identifies three separate legal arguments that the law's challengers needed to win on: "that they have suffered the sort of injury that gives them standing to sue; that the zeroing out of the tax penalty made the individual mandate unconstitutional; and that the rest of the law cannot stand without the individual mandate." From what we heard from five of the nine justices, the challengers might win on the first two but the whole shebang, the constitutionality of the law itself, will be upheld.
The court is expected to rule by June at the end of this session, and probably not any sooner.