Given all of the focus on severability in Texas v. California, it's worth bearing in mind how much the Supreme Court would have to get wrong in order to reach the issue of severability.
1. Standing is a real stretch. If people have it because they feel coerced even though they aren't, then standing is not the important constitutional principle that we thought it was, as Jonathan Adler ably explains.
2. Even if there is standing, Congress does not require an enumerated power to force no one to do anything, as Marty Lederman and I have separately explained.
3. Even if (1) there is standing and (2) Congress does require an enumerated power to force no one to do anything, the "mandate" remains better understood as a condition attached to a tax for purposes of Congress's taxing power. As explained in my analysis with Robert Cooter of the Taxing Clause -- which the Chief Justice's opinion in NFIB v. Sebelius tracks almost entirely -- exactions fall within the scope of Congress's taxing authority if but only if they are non-coercive, meaning that individuals subject to the exaction have a reasonable financial choice to reject what the government wants them to do and to pay the exaction instead. Reducing the payment for going without health insurance from around $700 (in NFIB) to $0 (now) makes it less coercive and therefore still a tax. In other words, what matters most for purposes of the Taxing Clause is whether an exaction is coercive, not whether it raises revenue. With non-$0 exactions, taxes raise revenue just because they are non-coercive. The two run together. With $0 exactions, taxes do not raise revenue even though they are not coercive. But the reason such exactions do not raise revenue is that they are $0, not that they are coercive and therefore outside the scope of the taxing power.
4. Even if (1) there is standing and (2) Congress does require an enumerated power to force no one to do anything and (3) the taxing power no longer supports the "mandate," the rest of the statute is severable --and obviously so -- for the reasons explained by many others.