Well if you haven,t got a nand backup you could use flash360 to make a backup of your nand via usb stick. Personally i would not risk it and would open it up and make a backup from the Jtag and make sure you compare the dumps so you know there good.
This post will help you a lot:
h**ps://docs.google.com/View?id=dnfmv5h_186pp2zddm