At the end of Marvel's Eternals, Ikarus lived up to his namesake. After he was forced to choose between his family and Arishem's great design, the Eternal could not bear to exist in a world where his love was in conflict with his duty, so he threw himself into the sun. Speaking to CBR, Eternals screenwriter Kaz Firpo confirmed this act did, indeed, kill Ikarus and offered a little insight into this decision.
"What is the melting point of an Eternal? How long does it take to literally melt an Eternal robot?" Firpo joked. "For what it's worth... yeah, it was always that. He can't bear to face his family after what he's done, which he realizes."
"I don't think that Ikarus even thinks that he's wrong. I think that he just has so much regret. He's very sorry. I think he's sorry for the way he lived his whole life on this planet, and that's a lot of burden to carry," he explained. "So really, that act is basically saying, 'I made a mistake, but I can't face my family, and I can't go on living.'"
"It began as an exile that I think, throughout the course of the filmmaking, really became something that needed to be definitive," he added. "It really is a moment of saying, 'It's sacrifice.' It's sort of saying, 'I can't serve the Eternals. If I can't serve the Celestials, and I can't be with my family, then I choose this third option,' which -- for him -- really is oblivion. So yeah, he dead."
Over the course of the film, Marvel's Eternals learn their true purpose: to protect life, allowing it to thrive on a planet, so that it generates the necessary energy that allows the next Celestial to be born. However, in the process of a Celestial's birth, all life on the host planet dies -- a sacrifice deemed necessary by Arishem. The Eternals are horrified to discover Arishem's grand design, particularly after they became so attached to humanity during their time on Earth.
All of them, that is, but one: Ikarus. Ikarus remained so committed to his duty to Arishem that he killed Ajak and led the rest of his family astray. Then, as Tiamut began to emerge, he actively fought the others as they attempted to prevent the Celestial's birth. In the end, Ikarus loved Sersi so much that he couldn't bring himself to stop her as she transformed Tiamut into marble. This act tore him apart; he had failed not only his sacred duty, but also his family. As a result, he could not longer live with himself, and thus destroyed himself by flying into the sun.
Marvel's Eternals is now in theaters.