The Atlantic’s Matt O’Brien had the smart idea of looking at how Wall Street reacted to this week’s Supreme Court hearings on the health reform law. And it seems that markets are betting on one of two outcomes — either the law will be allowed to stand or be repealed entirely.

Insurance companies have predicted that one possible outcome — in which the court strikes the mandate, but allows the rest of the law to stand — could lead to doomsday. If there was no penalty for not buying insurance, the thinking goes, only those who expect high health care costs would buy policies. That would likely mean the cost of health insurance would spike. More expensive premiums would, for insurance companies, likely mean fewer customers and less revenue.

Coming out of this week’s argument, however, health insurance investors actually look incredibly bullish on the Affordable Care Act’s future. O’Brien points out that Aetna’s stock soared in the 24 hours since oral arguments wrapped up. And that actually looks to be true for the five largest health insurance companies, all while the Dow Jones average has remained pretty flat:

This could, as O’Brien points out, be really good news for Obamacare — or really bad.

On the one hand, it could suggest that the insurance industry expects the law, with its mandate, to stand, bringing in 16 million new customers. On the other, this could be investors signaling that they think the justices will wipe the entire law off the books, relieving insurers of the requirement to accept very sick, less lucrative patients.

In oral arguments, the justices did seem skeptical about the idea of picking and choosing which parts of the health reform law would have to fall if the individual mandate went down. “A common reaction, across the bench, was that the Justices themselves did not want the onerous task of going through the remainder of the entire 2,700 pages of the law and deciding what to keep and what to throw out, and most seemed to think that should be left to Congress,” writes SCOTUSBlog’s Lyle Denniston. “They could not come together, however, on just what task they would send across the street for the lawmakers to perform.”

As for the insurance industry, America’s Health Insurance Plans spokesman Robert Zirkelbach says that plans have not changed in light of oral arguments. While they are looking at “planning for any potential Supreme Court ruling,” right now they continue to treat the Affordable Care Act as the law of the land.

“No one knows what they’re ultimately going to decide,” says Zirkelbach. “We’ll find out in June. In the meantime, our focus continues to be on implementing the new requirements in a way that will be the least disruptive and costly to consumers.”