When he gets to kaido, Kaido will be on the brink of death and I doubt zoro will be so badly injured that he can't deal with Kaido.
If big mom also goes down then maybe luffy will have to do it but Luffy + zoro vs kaido is overkill. Raid Kaido can't deal with Kiku and Raizou, what's he gonna do against luffy and Zoro. And people want law, kidd, drake, Hawkins, killer and Apoo to join. For what? To witness a lol troll diff fight?