I think they will throw the whole thing out, lock, stock and barrel. Roberts is the key figure for more reasons than one. However, if he votes with the majority, he will decide who writes the opinion. If they want to, each Justice could theoretically write their own concurring or dissenting opinion. They try hard, however, to join in one majority opinion because then it becomes clear what the law of the land is. No real precedent is set if the majority of the Justices vote the same way, but give different rational for their decision. And I think Roberts knows that this will be at least one of the decisions that define his court. He has a tough job trying to get very disparate views in line on this one. I think his instinct would be to throw out only the individual mandate and let the legislature wrestle with what is left over because his core belief is to not legislate from the bench. However, if he does that, I believe a number of Justices would fracture off from him. We would be left with a mess of concurring in part, dissenting in part, and agreeing and disagreeing in part because of the the legal bases for each aspect of the ruling. So in order to maintain his coalition on the right of the Court, I think he will grudgingly agree to strike the whole law. For the record, I think that is the correct decision because Congress failed to include a severability clause whereby the rest of the law would remain if part were struck and also because there would be an unfunded mess if they just chucked the individual mandate. Now let's sit back and see what the only 9 people whose opinion counts decide what to do.