doesnt have to be one individual
could die from a collection of attacks not a single one
or an outside party comes off to finish a wounded kaido
as far as am concerned
oden didnt have to lob off kaido 's head to prove he can kill him
kaido knew he could after giving him a scar/ damaging him significantly - if oden aimed for the head......
dude was in bandages for days and continues to have oden ptsd 20 yrs later.
thats all zoro needs to prove.
if he actually kills him tho
wont mind .
would have proved what I thought before he actually does it way before.