User blog comment:CNBA3/About E.N.D. Thought!/@comment-7418318-20140228113107

With Zeref's comments in chap 373 it made me think that anyone who killed E.N.D. would also die.

If the only way to kill E.N.D. is to die yourself, it would explain why Igneel was unwilling to make that sacrifice back then, since there's still the whole matter with the Dragon King Festival (I do not think the GMG had the real DKF and that the king was just assuming wrongly) to take care of, he decided to preserve his own life so he'd be still around when the right time to act came.