How long can H4 dependent stay in US after H1b travels back to India

How long can H4 dependent stay in US after H1b travels back to India?
My wife has just delivered a baby and she cannot travel to India for next 3 months. My project is getting over next month and I have to travel back to India. How long can my wife stay on H4 visa after I have left?

My wife has her visa and I 94 valid upto 2016.