User blog comment:Squedswag/E.N.D. Theory: Possibly that Nasu will stay alive even if he kills Zeref/@comment-2.42.96.115-20170108175713/@comment-30338537-20170108211156

Imagine a fully Demonized Gray getting inside Natsu to create antibodies :D

According to me, removing the Demon Seed will result in Natsu's death, as it is the Demonification that revived him (and thus keeps him alive) and removing a Seed will result in the loss of Demon/Dragon powers. If removing the seed was the answer, the Dragons may have opted to simply do so, but they knew the DS wouldn't be DS anymore without their Seeds.

But I do like the anti-Demon bodies theory. Perhaps Franmalth could return and do the job? :D Natsu probably wouldn't mind having to run around with a mushroom on his head ^^