The Eternals are god-like, to start, being a race of cosmic beings that are powerful in the universe. They've been living a low-key life for thousands of years, and now that they are about to debut in the Marvel Cinematic Universe, let's settle the question here on whether they are immortal and if they even die.
Are Eternals Immortal?
Given their name meaning immortal, it could be argued that Eternals could technically be immortal, and with technology, meaning they are not immortal per se, they just have certain abilities to remain alive for so long that they could be considered immortal.
Their origins are from the Celestials, ever-powerful beings of the universe responsible for the creation. The Eternals are the genetical winners of the lottery compared to the other race born with them at the same time, the genetically unstable Deviants.
The immortality of the Eternals is born from their very abilities to control and manipulate their atoms and molecules, the same ability which makes them invulnerable. Immortality does not wear them; they wear immortality as they have control over it. They are continuously conscious of the mental hold that they have on their physical form allowing them to be near immortal or effectively immortal.
They could be restored to life. The Eternals could do this even when their physiological structure of molecules is scattered. There's an activation chamber in Olympia where the Eternals could be reborn as who they are with all their memories still with them. Basically, like a cheat on death itself, they hold their presence through their minds.
Can the Eternals die?
Well, just being technically immortal, they could be killed as well, which could also be senseless because they could be brought to the activation chamber in Olympia to be recreated. Still, an Eternal can die and remain dead. An example would be Zuras, who killed himself in suicide after the Dark Celestials arrived, he was reborn but was murdered again by Thanos when the Mad Titan crushed his skull.
Speaking of Thanos, in the MCU, we see him die as well, in a different way, of course, as he was snapped by Tony Stark after the long battle for the Infinity Stones. He remains dead for all we know, dusted into pieces, along with his army, sitting in defeat.
One Eternal, however, remained in astral form despite having his physical body disintegrate. Kronos accidentally nebulized himself in a failed experiment with cosmic energy. Because of that, he became one with the universe, and he remains to be one of the most powerful beings still in existence in the universe.
The Eternals would grace the MCU in theaters on November 5, 2021.
Related: Eternals: Who is Thena and What does Her Sword Do?