I've been getting the distinct sense that Warren is triangulating for VP candidate. I think she recognizes that Sanders has the momentum but is unpalatable to establishment Dems while the Sanders camp is at "SANDERS ALWAYS but okay fine if we have to we'll stomach Warren". Warren's performance was the archetypal "I'm only the VP so I'm allowed to go off leash" debate. She cut into a lot of people but she only gave Sanders flesh wounds. I think she's still gunning for the nomination but I suspect she'd totally link up with the Sanders camp if that's what it took to get the superdelegates to be okay with a Sanders presidency.
I think Warren has to be President or remain in the Senate. As VP she would be too far outside of the policy-making machine that she is so good at. Bernie is all hat and no cattle... he has never gotten any serious legislation passed. He is a compelling speaker and an incredibly principled person. As VP he could take on the Big Picture issues and sway public opinion - as he has been doing in his campaign - but leave the practical aspects of the lawmaking to the people who have done it so well for so long. Warren is the wonk. Bernie is the message. Then we make Adam Schiff the leader of the Senate once Moscow Mitch is unelected by his constituency, and we can Get Some Shit Done, FDR-style.