Chopper says that Zoro is going to receive "many times over" the damage he had sustained before from Hakai. He can scarcely imagine what state Zoro would be in afterwards, as he was already completely paralysed even before the Mink medicine. He then pleads for Zoro not to die on them.
I think what is happening is that Zoro's body is confronting certain death, and Oda chose to make this allegory explicit by having Zoro come face to face with Death itself.
I think a route that Oda can take with this confrontation is: "Zoro will conquer Death itself to become the true King of the Underworld". Here's an example narrative scenario:
The Grim Reaper's scythe 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.
And/or by conquering Death, Zoro's body may be fully 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 battles 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.