Assuming Prop. 8 reaches the Supreme Court on the merits, which side has more to lose?
If the Court strikes down Prop. 8 as unconstitutional, its supporters will lose California, as well as forty-four other states that currently do not allow same-sex marriage, because bans would be unconstitutional nationwide.
The reverse is not true, though. If the Court upholds Prop. 8, its opponents will not lose the nation—only California. No federal constitutional right to same-sex marriage does not mean no state right. Other states could continue to allow same-sex marriage, although defense of such would be minus federal constitutional bases and prospective federal benefits for same-sex couples (e.g., tax) would be more remote.
In short, Prop. 8 supporters have far more to lose: they are risking the nation for one state, while opponents are risking one state for the nation. Ironically, if standing is not found, as has been widely discussed in the media, and the case does not go forward on the merits, there is a bright side for Prop. 8 supporters. A colossal risk will have been foreclosed and face saved, since supporters would not be giving up the fight voluntarily. Both sides could then regroup for the next fight, of many, no doubt.