In all likelihood, probably not much. Except, Democrats will likely scrap the proportional system they have now in favor of winner-take-all (particularly in the event of a brokered convention, and if the Democratic presidential nominee loses to John McCain this November), and revise penalties for states that break DNC rules.
That will not happen. The race would still be very close under winner take all anyway. For that matter each state party sets its own system and the vast majority would be opposed to switching, even if the DNC for some dumb reason wanted to lobby for winner take all. WTA is just too blatantly undemocratic and would piss too many people off.
