In a word, if the Supreme Court rules that Obamacare is constitutional, citizens should press their state governors and legislatures to nullify the law. You say, "Williams, the last time states got into this nullification business, it led to a war that cost 600,000 lives." Two things are different this time. First, most Americans are against Obamacare, and secondly, I don't believe that you could find a U.S. soldier who would follow a presidential order to descend on a state to round up or shoot down fellow Americans because they refuse to follow a congressional order to buy health insurance.
Congress has already gone far beyond the powers delegated to it by the Constitution. In Federalist No. 45, Madison explained: "The powers delegated by the proposed Constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite." That vision has been turned on its head; it's the federal government whose powers are numerous and indefinite, and those of the state are now few and defined.
Former slave Frederick Douglass advised: "Find out just what people will submit to and you have found out the exact amount of injustice and wrong which will be imposed upon them. ... The limits of tyrants are prescribed by the endurance of those whom they oppress."