Btw I don't believe that Zoro's attack would have killed Kaido but it would have done significant damage hence why the attack was portrayed as something Kaido has to avoid.
Hence why Oda had Kaido shiver, same Kaido who was welcoming all the attacks from Luffy, from Kidd, from Killer even gamma knife from Law without an ounce of worry.
And Big Mom was also not worried about those attacks, to Big Mom it was Kaido playing with his food.
It is not just my opinion, it is the way story telling works, the way Oda has set up those attacks.
Zoro's Attack that Kaido dodged >>> Red Roc >>> All other attacks on Roof top so far.
@sanjikun @KAIDO D. STRONGER
I don't know how much damage it would have done exactly but certainly more than that combined attack from Scabbards that failed to open the scar because Kaido even welcomed that attack.
So I would say it would significantly wound him, perhaps as much as Oden wounded him perhaps slightly less.