Equal rights. Not equal abs.
If you believe that the modern-day Supreme Court is averse to setting earthshattering precedent (and there's much ado about this topic), then one likely outcome is that they will say that the plaintiffs in the Prop 8 case lack standing in the case. Since the appellate court already upheld that law being overturned, this would mean that California would once again allow gay marriage. I think.
The DOMA case is a bit more interesting. Maybe the Supreme Court could find a narrow technicality to throw out the law, in a vain attempt not to establish a fundamental right to gay marriage. Let's take that as a given, for the sake of discussion, and ponder what the outcome would be.
In effect, you'd have full Federal recognition of gay marriages, which would then be legal to get in a minority of states. In other states, however, you wouldn't be able to get married. But what if you got married in another state and moved into a state that refused to recognize those marriages? That will set the ground for yet another lawsuit which would inevitably find its way up to the Supreme Court. *That* case would be harder to skip on a technicality, and would probably settle things once and for good.
Maybe.