The main reason an incredibly prosperous land like Wano fell into the shambles that it is today is mainly because of Orochi. Kaidou is only a supporter that aided him in destroying it. It makes zero sense for someone like Orochi who has cause Wano so much strife to be disposed off so easily. Also you've gotta ask yourself the question why Oda even bothered to give a weakling like Orochi a devil fruit as rare and powerful as the yamato no orochi if he was just going to dispose of him the way he did.
With current sequence of events, I'm not really sure how Oda uses Orochi but Orochi imo still has a trump card at his disposal, which is the CP0. Who knows, we could see a situation in which Orochi allies with the marines and the current situation with the Samurai and the SH alliance going after Kaidou is very advantageous for him particularly if he's able to get some sort of marine backing