User blog comment:Martialmaniac/How will Gon regain his Nen?/@comment-25814498-20151009220043/@comment-5780397-20151010165822

My hope exactly. Actually, I like Jajanken a lot, but he could use a more "battle-efficient" ability.

Well, that was the restriction he had (unconsciously?) imposed upon himself, so perhaps it was considered unrelated to his physical condition. I mean, his vow probably combined "bodily decayment and inability to use Nen", and Nanika only reversed the former. I don't think he could have obtained all that power "just" by sacrificing himself. Besides, someone spoke about a Covenant and a Restriction, right? I think the covenant was "Give me power and destroy my body" and the restriction was "I will never use Nen again afterwards".