I'm not predicting anything. I would like lay out a possible way this could play out. The Dems could split resulting in both Hilary and Obama being on the ballet come November. That is that there are two Democratic presidential candidates. This has happened a few times in U.S. history, most notably in 1860, when there were three Democratic presidential candidates, Stephen Douglas, John Bell, and John Breckinridge. It also happened to the Republicans where former president Theodore Roosevelt ran in 1912 as an independent Republican - the so called "Bull Moose" party.
Before the McCainiacs get all excited, I should point out that this may not play to McCain's advantage. If he were to pick a very liberal VP, he could alienate his base. In which case, many conservatives could defect to Bob Barr, the Libertarian candidate. Barr is not really a Libertarian at all, but a very conservative Republican who felt like he was squeezed out of his own party. With a united Demcratic party, conservatives will likely rally behind McCain, because both Dem candidates are so radically liberal that they would do great damage. But if the Dems are divided, all bets are off and we could end up with four presidential candidates getting electorial votes. Is this likely, no, but what did happen in 1860 wasn't likely either.