I keep mentioning that "Zoro will conquer Death itself to become the true King of the Underworld". Well, here's a narrative scenario that I think Oda could take with that route:
The Grim Reaper's sycthe will "reap" Zoro and send him to the Underworld.
There he will fight against the Lord of the Underworld (Enma). He will triumph and become the true King of the Underworld.
Zoro will then return to the land of the living, triumphant and invincible.
By triumphing over the Lord of the Underworld (Enma), he may also have forged Enma into a Black Blade as a result.
The Zoro who returns would be fully healed and restored to peak condition.
Zoro's battle with in the Underworld may be physical (as in Zoro's body actually disappears), spiritual (Zoro's soul leaves his body) or purely mental (Zoro hallucinates all of this). (Perhaps as Zoro's soul/mind battle in the Underworld, Zoro's body feels the full effects of the double pain and damage he took).
Regardless of the form it takes, the battle will signal Zoro's struggle with and triumph over Death and harken back to the declaration Zoro made all the way back in Arlong Park:
The Zoro who has triumphed over Death would be significantly stronger than he is now.
@ShishioIsBack,
@Geo,
@KiriNigiri,
@Den_Den_Mushi,
@style,
@spawn,
@ConquistadoR.