The Prop 8 trial will most likely reach the Supreme Court around summer of next year, which means that if we're lucky, the SCOTUS will rule it unconstitutional and their decision will be affective across the entire country.
http://www.prop8trialtracker.com/2011/11/23/where-things-stand-with-the-prop-8-trial/
And what if they rule that it is constitutional?
Maybe I am too much of an optimist, but I cannot see that happening. Appeals courts (such as the USSC) do not, under normal circumstances, hear new evidence. (The exception is when there is a request for a new trial based on new evidence that was not available in the original trial. In that case, they are not retrying the case, only deciding if the new evidence is significant enough to warrant a new trial.) The only evidence appeals courts hear is what was brought up at trial, and evidence is only heard through the record. (Witnesses do not testify again.)
I followed the Prop 8 trial at the time, and I've read Judge Walker's opinion. The pro-Prop 8 side presented no real evidence in favor of banning SSM. Without such evidence, the appeals court does not have much of a basis to rule in favor of Prop 8.
As an aside, I am not sure that even if the USSC ruled against Prop 8, it would make SSM legal across the country. The 9th Circuit based their ruling on the fact that same-sex couples had marriage rights in CA before Prop 8 passed. It was more an issue of "taking away existing rights" rather than an equal protection issue.
