Well, i can't explain in the best way but i will point out the factors which contribute to her survival.
1) katsuya is not only present and assisting, tsunade had the energy and strength left to summon.
2) she is still regenerating her cells rapidly?
3) tsuchukage will not accept whatever life saving technique tsunade offers in order that she may live and that he now dies upon his redemption before gaara. (Prediction)
4) naruto appears and life forces up those mokuton trees with his boss chakra modes. Everyone miraculously heals and has minty fresh breath.
5) HQ uses ftg or some fallback to rescue the kages and recouperate.
6) orochimaru does something unexpected and silly.
7) Karin does something unexpected and silly.