When the frogs say Naruto is going to die, it's more probably in the metaphorical sense. I think they could put him into a deathlike state where he has no internal energy left and has to pull energy from his surrounding to allow him to become senstive to sage chakra.
I don't think he will use "Hermit Mode" but more likely some sort of technique unique to himself.
With Sasuke and the eight tails, Sasuke will definatly win, but it will be the hardest battle he has ever participated in.
Also wonder what Pein is going to do when he finds Naruto gone?