User blog comment:B214/Volume 21 info & spoilers/@comment-99.118.13.217-20160613135349/@comment-1359322-20160613144533

I know that's why i replied only to the permanent sealing part.

Besides what the anon is saying isn't logical from the start anyway cause he's literally demanding the author to just kill everyone. He may not have listed all but the resulting effect is still everyone dying.

If Gasper dies then Valerie would be defenseless, even if she has the Holy Cross with her, she has zero fighting experience. She would die before she can even regain her Holy Grail. In that situation the Scale Mail army and Evil Dragon army will expand endlessly overwhelming everyone and kill them.

On the other side, which is Valerie successfully regaining her Holy Grail, she would ignore the risk towards her own body and revive Gasper as well as his close friends so everyone would return back to live in the end.

So simply killing them is meaningless from the start. You can even say one of the method of seal without dying can be a method to avoid using the Holy Grail to revive important characters like Azazel and Sirzechs.