If SCOTUS does knock down DOMA Section 3, that will put an enormous amount of pressure on the purple and pale-red states. Same-sex couples in Kansas will go to Iowa to get married. When they come home, they will be half-married—married in the eyes of the federal government and their families, but not married in the eyes of Kansas. I can tell you from personal experience that when colleagues, neighbors, friends, and family members hear about the small indignities and injustices of being only half-married, when they realize how ordinary you and your spouse are, they get outraged that you’re being denied full marriage recognition. Businesses will get annoyed that they have to track this dual-marriage status for their employees, and will start to pressure their legislators to change. Lawsuits will bubble up as people sue Kansas (and Colorado, and Ohio, and Oklahoma) to have their “foreign” (i.e., out-of-state) marriages recognized at home.
But here’s what’s more important: The Supreme Court is not the final arbiter of all things good and just (thank God!). Or even of all things political. If Kennedy loses his nerve, Congress can and will repeal DOMA—if not this term, then the next time the House, Senate, and presidency are all held by Democrats. And even if the Supreme Court issues a mean ruling on Perry—saying there's no fundamental right to marry and that California voters had every right to pass an amendment yanking equal marriage rights away—the Court will take it back in 15 years, when only ten Southern states are left banning recognition of same-sex marriages. The Court only took 17 years to overturn its ruling upholding sodomy laws in Bowers (which was a knife in the heart at the time, and pretty quickly became an international embarrassment). This one will come just as quickly, or even more so.