Ok, how about this. when sasori's grand mother used the jutsu to heal sakura, her life was supposed to end with the use of that jutsu. Transfer one life to another. That if proof that it is possible to use a life threatening jutsu and still live. Also, the kyuubi has been shown to regenerate damaged tissue as shown with Naruto. If my theory is correct, and the 4th did indeed seal the dark half of the kyuubi within himself, it is very well possible the 4th could have survived. With the accelerated healing of the kyuubi, as well as a strong desire to live, the 4th could have survived a supposedly ' fatal jutsu'.
The 4th could not have lost his life automatically. If this is so, how was it that the 4th was able to put the combination for the kyuubi seal in a scroll? How was the 4th able to relay his wishes to the villagers of konoha, in that he did not wish for Naruto to be viewed as monster, but as a hero? No, the 4th did not die automatically after using the jutsu. The effects were gradual, and I feel that the dark half of the kyuubi slowed the process down further. If he did in fact die, then it is possible that the dark half of the kyuubi resurrected him, and transformed him.
first paragraph chiyo didn't die because sakura was alive but really wounded fattally wounded that is why chiyo didn't die, the jutsu only took half the energy life force.