I understand that but this is not the first time a character has "needed to be killed" but hasn't. A lot of Luffy's thing is robbing people of their dreams so I think this war will end with Kaido humiliated by being dragged out in front of Wano in chains.
In my opinion giving Kaido the death he wants would be very out of character for the manga. Especially if its a Straw Hat doing it. I'm just personally going to go with the whole Momotaro thing where Momo chained the demon and brought him back home rather than slaying him.
However, outside of imprisonment in Wano or Suicide, I will agree Zoro is one of the front runners. The only other one I can think of would be Big Mom because he owes her a "life debt" so her killing him and saying the debts repaid does seem like something oda would do. But I'm still going with imprisonment because I personally think it fits better with humiliating Kaido.