User blog comment:IamJakuhoRaikoben/Chapter 247:Right Beside Each Other, Review./@comment-5799066-20110820150339/@comment-3987368-20110820185145

I know but I wasn't referring to direct physical combat since the spell that killed Zancrow seemed more like an 'instant-death' spell like from Final Fantasy or something.

Zeref looked like he was in a mental state when that happened (but I could be wrong, it was just his eyes that make me think so) and could theoretically enter such a state again.

Hades wants to use Zeref for his plan but Zeref (seemingly) wants to repent for his actions and could get angry at this and use the spell once again, or do something to that effect. If not kill Hades, at least disable him or something, I'd think.