So yes, there may be a referendum if the opponents of gay marriage gather enough signatures… which is probable. That means we won’t know the final results of this struggle until November.
If they don’t pursue the referendum or don’t gather enough signatures, the other option opponents have is the ballot initiative to define marriage as one man/one woman, but that wouldn’t prevent gay marriages from happening starting June 7th, which would place Washington in the same position as California regarding Prop 8: that initiative would remove already-existing rights from a group of people with no valid rationale for doing so, which the 9th Circuit has already declared to be an unconstitutional act.
They pretty much need to go for the referendum. Considering how many of the major employers in Washington have expressed support for gay marriage, it will be interesting to see what results they get.