If they strike it down Obama should hit the court hard for being so blindingly partisan. Obviously packing the court isn't going to work, but he should definitely go after them for horrible rulings like Citizens United.
I would submit that the Supreme Court striking down the health care law could be framed as a FAR more partisan act than Citizens United. The McCain-Feingold law was a bipartisan piece of legislation signed into law by President Bush. The Citizens United decision was 5-4. All five Justices in the majority were appointed by Republican Presidents, but so was one of the dissenting Justices (John Paul Stevens).
Contrast that with the Affordable Health Choices Act. First off, Ginsburg, Breyer, Sotomayor and Kagan are going to uphold the law so the only way it is going to be struck down is 5-4, with the five Justices GOP appointed (Roberts, Scalia, Thomas, Alito, Kennedy) in the majority and the four Democratic appointed Justices dissenting. It is the signature domestic achievement of the incumbent Democratic President (Obama), whereas I highly doubt President Bush would name McCain-Feingold among his most important accomplishments. And unlike the bipartisan McCain-Feingold, the Affordable Health Choices Act passed with almost no GOP support.