I wouldn't be so quick to count Gillibrand out as a potential 2016 running mate. She'd be a solid choice for any nominee.
Gillibrand and Klobuchar will be the frontrunners for Dem. VP nominee in 2016, if the presidential nominee is a man.
I'd say there's a >90% chance that the 2016 Democratic ticket will have a woman on it. If not as presidential nominee, then as vice presidential nominee.
Some of you youngins don't understand how quickly things have changed. We've rapidly transitioned from the default assumption being that both parties will nominate white males for president and VP to this new assumption that white male = "boring", and presidential nominees should pick women or minorities in order to generate "excitement" for the ticket.
This is particularly true for the Dems. I can't tell you how many Democrats I talked to in the 2008 cycle who explicitly cited Clinton's second X chromosome and Obama's skin color as reasons to support them over other Democrats. There's a lingering feeling of unfinished business among many Dems for getting a woman on a winning national ticket, and that'll result in a woman on the ticket in '16. (And will probably continue at least until we have a female president.)