Kaido has already defeated Luffy 3 times during the war. Oda even declared Kaido the winner.
With that said, just because a character is defeated doesn't mean they can't return. Luffy returned to battle after every defeat. He even returned after death.
Oda could have Luffy defeat Kaido during their latest clash and have Kaido unconscious on the ground. Then have the samurais and pirates celebrate Luffy's win. During this time the Wano citizens still don't know what happened. They didn't see Kaido defeat because he fell into the same hole as Big Mom.
After 10 minutes or so have Kaido regain consciousness thanks to his awakening. Kaido is enraged because he has lost everything so he decides to attack the Wano capital for revenge. If he's going to lose everything so should Wano. He turn Wano into a literal hell with his fire flame dragon mode.
The samurais and pirates decide to head to the capitol to stop Kaido. Unfortunately, Luffy is too weak and tired to fight. He has run out of energy and doesn't have enough power to recover.
That's when Zoro regain consciousness and head to the capital to face Kaido. As Zoro cuts through the flame with his fire cutting technique he looks like the King of Hell to Wano citizens. Some citizens realize Zoro looks like the former Ringo samurai and Ryuma. Zoro forge a black blade and kill Kaido in his fire flame dragon mode with a KoH Dragon Style upgraded flying dragon blaze attack. They see Zoro as the new Ryuma, god of blade.
The World government watched the battle and decided to leave Wano alone because they know what the first Ryuma did to them.