My guess has been that Kennedy is the decisive Justice, and we get a 5-4 decision. I've heard some people say that Roberts will vote with the majority if Kennedy does, which I guess I wouldn't rule out -- for all I know, Roberts might not care to vote with the right-wingers if the law is going to get upheld anyway. But that still makes Kennedy decisive.
If I have any idea how health care reform efforts should proceed if the Supreme Court strikes down the whole law, it's via Medicare expansion. Medicare for All should be a goal that our presidential candidates announce support for. (I could easily see the incentives in primaries supporting this -- if the other candidates aren't willing to go there, you should go there and people will like you better.) The reach is always further than the grasp, so next time we're in power, we end up having to make a bunch of compromises with interest groups and pass Medicare for people under 25 or something, and then a couple decades later the middle of the donut gets filled in.
Again, losing this court case will be an awful defeat. Scott Lemieux is right as far as I can tell -- there's no silver lining here. But the thing I tell myself about these things is that at one point, America had slavery. People were allowed to own other people, buy them, whip them, and sell their children. And somehow, that stopped. Having a disastrous health care system is going to be easier to fix than slavery. I don't even think we'll have to fight a bloody war with over a half million casualties. There might be setbacks that destroy millions of person-years of work, but what you do after the setbacks is start committing person-years to another shot at making things better.