It is obvious there is a solid four for upholding the law.
In my opinion though only Thomas is certain to vote to strike down the law. This mean the liberals only need to pick off one of Alito,Scalia,Roberts,or Kennedy to approve the law. Kennedy is always a swing vote, and the remainder have not always been in lock step with conservative principles. My gut says Kennedy and Roberts join the lib 4 to support the law 6-3. I pray that I am wrong.
I know by "law" you mean Obamacare, but I had to do a double-take to get that. More on that below.
Unfortunately, as you point out, the four bad guys only need one of the remaining five to get their way. My take, as yours: most likely Kennedy - game, set, and match (but the tourney isn't over at that point - if SCOTUS blows it, the states must do as Idaho did: nullify Obamacare and exempt its citizens from its mandates). If for some reason, Kennedy has risen up the right side of the bed the day of the decision, then we still may have a Roberts problem. Like you, I see Roberts, sadly, upholding the bill (at least on the Obamacare decision) because he is apparently loathe to overturn the legislature.
Back to what we call "law." The highest Law of the Land of course is the U.S. Constitution which trumps any other law that violates it. I'm sure you know this, but it's probably worth saying that in this sense, this "solid four" (or "socialist four") is for overturning the Law of the Land in favor of said "laws" like Obamacare that helps create a Socialist state. Because Obamacare is illegal (outside U.S. Constitutional bounds) and unjust (wrongly interfering with individual liberty) it is, therefore, as Augustine and Blackstone say below, NO LAW.
More on this below if interested from the Philosophy of Law:
The strongest form of the Overlap Thesis underlies the classical naturalism of Aquinas and Blackstone. As Blackstone describes the thesis, "This law of nature, being co-eval with mankind and dictated by God himself, is of course superior in obligation to any other. It is binding over all the globe, in all countries, and at all times: no human laws are of any validity, if contrary to this; and such of them as are valid derive all their force, and all their authority, mediately or immediately, from this original" (1979, p. 41). In this passage, Blackstone articulates the two claims that constitute the theoretical core of classical naturalism: 1) there can be no legally valid standards that conflict with the natural law; and 2) all valid laws derive what force and authority they have from the natural law. On this view, to paraphrase Augustine, an unjust law is no law at all. http://www.threes.com/index.php?option=com_content&view=article&id=1409:philosophy-of-law&catid=75:philosophy&Itemid=60