I have trouble beliving that would be the case. Gay Marriage bans have passed in every single state they have been on the ballot, including blue states.
Frankly, if you ARE right, then I don't see what the point of trying to pass a Constitutional Amendment is anyway, before or after, because it won't pass. They can and would use the same tactics as they would to keep it from passing before hand then afterwards.
Right now the benefit to our side is that we are conserving the definition once the Court rules we will then be no conserving but reacting. Conserving/conservative has more appeal than reacting/reactionary, at least most of the time.
And frankly if Vermont wants gay marriage and Oklahoma doesn't and I really thought there was a way to sustain that, it would be fine with me. I really don't care what people in Vermont do.