After Super Tuesday it's the only reasonable option ...

Prediction: Biden + Warren.
Biden continues his ascent in the polls and takes the presidential nomination at the Democratic National Convention. Warren is selected as his running mate after she abandons presidential race given her poor performance in the polls and her loss in the primary in her home state (MA).

Rationale: Democratic moderates and conservatives are 'scared' of Sanders's "democratic socialism". Warren's politics aren't all that different but her presentation is far less strident and therefore less 'scary', thereby attracting those moderates and conservatives (and true lefties) in the party; moreover she can easily attract the female vote across most persuasions.
Biden already has the ethnic vote wrapped up. (Now if he'd only lose the gaffes.)

This is the only Democratic ticket which stands a chance of defeating Trump and his ilk qua coterie of klutzes and saving America's face and future across the world ... short of a mystical savior arising from another dimension. It may also have the salutary effect of getting decent candidates elected to the House and Senate and derailing the train wreck of the past decade.

Remember: You heard it here first.

Saving grace: If it doesn't come to pass, you'll have forgotten that I said it ... because you'll have too many other things to worry about when the Antichrist is inaugurated for another 4 years.