The Supreme Court has many options in the Prop 8 case.

How many? Marty Lederman says he'd originally thought there were 5: 1. no standing, 2. uphold Prop 8 on the merits, 3. reject Prop 8 in a way that relates only to California, 4. reject Prop 8 in a way that would also require gay marriage in the 8 states that have civil unions for gay couples, and 5. find a constitutional right to same-sex marriage that would apply throughout the country. Now, he sees 2 more options: 6. dismiss the petition (decide it was a mistake to take the case at all), and 7. vacate  and remand for reconsideration in light of whatever it does in the DOMA case.

Lederman thinks you can't tell from the oral argument, in which it seemed that at least some of the Justices were struggling to try to figure out what to do, but he thinks 2, 3, 5, and 7 are unlikely and 6 is also pretty unlikely.

So what about 1 (standing)?

... Justice Kennedy, expressed concern that if the Court were to hold that the Proposition 8 proponents lack Article III standing because they are not agents of the state of California... such a ruling might invite executive officials in California to effectively “thwart the initiative process” (Justice Kennedy’s words), simply by refusing to appeal lower court rulings declaring that such initiatives are invalid....

And 4 (reaching the merits and covering 8 states)?

To be sure, Justice Kennedy stated that it would be “very odd” for California to in effect be “penalized” for being “more open to protecting same-sex couples than almost any State in the Union.”  To like effect, Justice Sotomayor said that there would be an “irony” if “States that do more [for same-sex couples] have less rights.”...

But that objection doesn’t quite capture the fundamental nature of the eight-state argument—namely, that it’s an underinclusiveness argument of the sort the Court often invokes to explain why a state’s defense of a law is inadequate. 

Actually, everything seems unlikely and unsatisfying... and yet there will be a decision. I note that there could be an outcome without any rationale commanding a majority. That should be considered the 8th possibility. The 8th option for Prop 8.