The Court really shouldn't even be taking this issue up. The standing issue is the most glaring issue here. In essence, the individual mandate is a sternly worded letter from the federal government (or not even that). If the federal government just randomly says to do something and there is no penalty or action at all on an individual, there is no controversy. If I only looked at the appeal itself, which includes a number of states and the House as intervenor-defendants, I would say the case was improvidently granted. But the real issue is that the district court should have never heard the case to begin with and the Fifth Circuit should have ruled accordingly. This case really makes a mockery of the issue of standing if it's heard on the merits, but I expect that it will.
Based on ACB's testimony & what we saw earlier this year re: severability in Seila Law v. CFPB, the Roberts Court won't be wrecking Obamacare anytime soon. I think we'll get a 5-4 ruling to grant the plaintiffs' standing & find the residual individual mandate unconstitutional (with Thomas, Alito, Gorsuch, Kavanaugh, & ACB in the majority + Roberts, Breyer, Sotomayor, & Kagan dissenting), but 7-2 (with only Thomas & Gorsuch dissenting) that it's severable from the rest of the law.
I've been sufficiently persuaded that Kavanaugh will vote for severability, but Alito definitely will not. It will not be 7-2. Alito voted with the dissent in 2012 to strike down the entire law. You're thinking of another Justice that votes in good faith based on objective principles. The closest ideology for Justice Alito that I can think of is "conservative Republican". I did see Barrett's comments on severability. That or Kavanaugh may save most of the law, but it does not mean other portions of the law are safe. I've said before and I still maintain that eliminating the individual mandate will likely take down guaranteed issue and community rating (i.e. protections for preexisting conditions, age, gender, etc.). That will have effectively gutted the Affordable Care Act.