According to Reuters, Justice Ruth Bader Ginsburg "vowed to resist any pressure to retire that might come from liberals who want to ensure that Democratic President Barack Obama can pick her successor before the November 2016 presidential election."
I love Ginsburg (Jeffrey Toobin's profile of her in a recent issue of The New Yorker, locked behind the paywall now, is a good place to start if you want to learn more about her), but if this report is true Ginsburg is being shockingly reckless. We've seen how quickly so much can be undone in a short time by the Supreme Court having Roberts replace O'Connor, I'd be stunned if Ginsburg didn't ultimately realize how much of her life's work could unravel in just a few years if her seat was vacated with a conservative President in office.
Lots of ifs, but that's just the point: Obama is President now, she is still healthy now, these are things we know. 2016-2020 is an unknown.