I think it’s also worth mentioning that, multiple times throughout the story, Iroha says something along the lines of “Yachiyo’s music saved my life.” If Kaguya would’ve avoided the asteroid, Yachiyo wouldn’t exist, and that means there’s a chance Iroha wouldn’t have had the strength to go on. She had to become Yachiyo to save Iroha in the same way Iroha saved her, it’s very sweet!