How did Kushina survive the extraction of the Kyuubi? While Kushina gave birth to Naruto, Tobi came in and used her weakness to extract the Kyuubi. That was the first shown event, where a Jinchuriki survived the extraction of the tailed beast. How could Kushina survive that?
Kushina survived the bijuu extraction due to the Uzumaki clan's incredibly strong life force. 

(Chapter 501)
  


Spoiler Block:


   (Chapter 579)