For the first time I'm also gonna disagree with Houkai here.

Like the previous post says. Vrtra's sister might be alive. He also took extra care not to endanger anyone not directly involved in the quest.

Furthermore Endwalker's MSQ ended in 6.0. They shouldn't hang so tightly at the same message anymore. This is a MMO. It's been 8 years of trying to write a story based around the same theme. It's time to turn the page because it would be exponentially difficult to come up with more ideas while imposing that kind of thematic limitation.