Since I was referring to the party's nomination, and not the general election, why do you think this is relevant?
Having been a VP gave Mondale a sizeable leg up in getting the nomination.
Mondale was actually the VP however. If Hill took the offer and Obama lost she would only have been the VP nominee, never the VP.
Honestly, I don't think it would matter with Hillary. If she decides to run in '16 she'll get the nod regardless of her current decision