Eternals

The Eternals learn the truth about Arishem's design and split: some accept it, some refuse. Ajak, their leader and Arishem's direct link, decides — after watching humanity survive the Blip and then reverse it — that Earth deserves to live and the Emergence should be stopped.

Why does Ikaris kill her? Because he sides with Arishem. He has known the truth for centuries and believes the Celestials' design is above question: billions of lives across the cosmos depend on new Celestials being born, and one planet is an acceptable price. He kills Ajak for treason by feeding her to Deviants, and Gilgamesh dies in a Deviant fight partly through his interference.

The rest stop the emergence of Tiamut. Why Ikaris flies into the sun: having failed, he faces the fact that he murdered his own family for a doctrine, while in love with Sersi, who is now leading the opposition. He cannot kill her.

It's suicide, plainly.

Why does Arishem take some of them for judgment? Because they disobeyed — a Celestial that would have been born was destroyed. He takes Sersi, Kingo, and Phastos to examine their memories and decide whether humanity is worth preserving, promising to return with a verdict.

He hasn't. That thread is entirely open.

The reason to care: the half-emerged Celestial corpse remains in the Indian Ocean, and it is made of adamantium.

That is the film's real legacy — and it makes Wolverine's metal possible in this universe.