Hillary's got to do some thinking on this one, as Obama has proven adept at reaching a cohort with whom she just doesn't seem to be able to connect with. Having said that, there's no reason to think that McCain will be any more successful than her with the under 30's so my best guess is that a lot of them will vote with their feet as they have done previously, so her inability to reach into this group might not be terminal to her chances.
If she gets the nomination through the back door of the party machinary she is pretty well going to be forced into offering Obama the ticket or seriously risk opening up a wound right across the party. The problem of course is that the two of them don't really seem to get on despite having quite a lot of seemingly common ground. There's no gurantee of course that he'd accept the offer as he's young enough to sit it out rather than risk getting stained with what might be a rocky Presidency. The ethnic vote that he'd bring will vote Democrat anyway, and Hillary has a significant base with blacks and hispanics from the previous Clinton Presidency, so delivering this constituency wouldn't be part of his appeal. His strength would lie in bringing in younger voters, but some how or other she's got to find a way of winning some southern states, principally Florida. I'm not sure an Illinois Senator is going to do that for her. He might very well have out-performed her in all the southern states bar Texas, but the reality is that few will vote Democrat anyway. The blue collar core vote should deliver either of them the industrialised northern states, and the democrat vote tends to hold in the more outward looking eastern seaboard and California
What either of them will need is a Southerner, in much the same way as Kennedy had to take Johnson despite Stevenson being the preferred party candidate. In fact I've got a feeling that nomination was settled at the convention when Bobby Kennedy worked out that California was going to swing it on the first ballot and did some conference floor hot footing in order to secure the super delegates support.
It's inconceivable that Obama would want Hillary on his ticket, as Grasshopper points out, she'd be more likely to cost him the election in the areas where he needs to be strong, and represents a risk he wouldn't need to take. He'd need someone with a degree of gravitas and experience, but is again looking towards someone with a southern base I'd have thought.
There has to be a chance however that McCain might take Guiliani yet, so we could have some fun in this direction still, though logic dictates that he'll need someone to appease the conservative wing of the Republicans even though it's difficult to envisage them voting any other way and he might decide he can take them for granted. That being so, someone like Guliani who could potentially draw in some of the anti Clinton Democrat vote would have an appeal, especially in New York, which would be a fascinating sub plot
I think the Republicans have let it be known that they'd rather face Obama than Clinton Ven. Mind you, it could be an elaborate bluff. I'm far from convinced that Obama has the substance and over a prolonged campaign, they'd fancy their chances of exposing this. Tony Blair might have got away with running a campaign on nebulous things such as 'values' 'visions' and 'things can only get better' etc but it's harder to pull this stunt with the lead times involved in the states