Nothing changed regarding Kaidou's character.
Everything that we are seeing now was one of the most predictable routes for his character. The moment you saw his introduction, the moment characters like Brago from Gash Bell!, Mewtwo from Pokémon or BlackWarGreymon from Digimon should have come to mind —incredibly powerful monsters who were villains yet grew respect for the main character to the point of ultimately losing their threat after changing their mind (plus some of them questioned their life, or developed misanthropy, or were experimented on and/or directly manmade. While people found it strange that he was laughing with Luffy and respecting him, I expected it for years. On top of it, the way some of you guys speak of Kaidou's dream make it feel like he isn't a person who can change even though his obsession with death was probably based on his boredom with the world; if anything, his defeat against the returned Joy Boy should be something with potential to change his view on life —what happened to Brago, what happened to Mewtwo, what happened to BlackWarGreymon, what happened to whatever character fitting this trope you may want to think about.
Kaidou doesn't need to die. He may die, obviously that's one of the possibilities on the table, but he doesn't "need to". His dream means shit (dreams change) and Oda has it easy if he just keeps following the same route he has been working on with the character.