People are right to point out that Luffy is still the main character and needs to beat Kaido. Same way that the story points to Zoro (at the least) cutting Kaido, and Kid and Law playing a part in his defeat, the story also needs this to be the moment that Luffy comes into his own as a Great Pirate and gets ready to hand his hat back to Shanks. That means Luffy has to prove himself the strongest on the ally side, the main reason that Kaido is defeated and the one to beat him.
Having said all that, I still think that the above can happen, and that Zoro can kill Kaido.
Zoro killing Kaido (should it happen) will be in dragon form. Dragon Kaido will not be as strong as hybrid Kaido.
What Oda would need to do is have Luffy be the one who performs the best against, and overcomes, hybrid Kaido. I think Oda will need to write it as Luffy clearly having hybrid Kaido beaten, maybe even have Kaido acknowledge that. Then have Dragon Kaido flying off to destroy the Flower Capital as a last throw of the dice, with him acknowledging that he can’t beat Luffy, and that’s where he could have Zoro come in and kill him. Hard to write, because he’d need to have a good way of keeping Luffy out of that final piece of action- Big Mom coming into play and Luffy needing to hold her off? Something like that- but it can be done.
And I’d also be wanting Zoro to have beaten King previously so that all he’s doing isn’t just killing wounded Kaido.