WARNING: The following contains major spoilers for Marvels X #6 by Alex Ross, Jim Krueger, Well-Bee, and VC's Cory Petit, on sale now.
Marvels X has seen more than its fair share of tragedy splashed across its pages. In a world where the Terrigen Mists have been unleashed on the globe and turned many into raging mutates, there is only one hope for a cure: David Jarrett, a young man who is the one and only human left on the planet. David has plenty of heroes protecting him, and they're more than willing to go to any lengths to ensure his survival.
Inside the Baxter Building, the White Coats have been working overtime to begin developing a cure for the worldwide superpowered outbreak. Their time isn't just running out, it's already over. The building has been breached by hordes of mutates hellbent on killing Reed Richards, who they blame for their condition, as well as any other hero or vigilante they can get their hands on.
The battle inside is raging, with a slew of other Avengers fighting as hard as they can to stave off the mutates. As they shoot their way through as many of the invaders as they can, Black Widow and Hawkeye discuss a defense system that Reed has in place. Natasha asks if they're ready, and Clint tells her to hold on. Reed calls for the protocol to begin, and reminds everyone to be mindful of the tech he gave them earlier.
"There's a place called the Negative Zone... filled with monsters. Reed says it's got plenty of room for more," David narrates as the room is warped and torn open to reveal a twisted and fluid dimension outside of our own. The tech that they are wearing prevents the heroes and David from being pulled into the wormhole, but these safeguards don't protect against the mutates, which David learns when one nearly yanks him free from the ground. It's then that Ikaris makes the ultimate sacrifice.
Ikaris, an Eternal, flew into the mutant that was heading for David and carried it with his fists straight through into the Negative Zone. Ikaris then begins flying back towards the tear in space, but when another one of the mutants makes a beeline for David he makes a choice that leaves him arguably worse than dead. Ikaris' eyes "glowed like a god's would [and] blasted through the portal," as David tells it, "and destroyed whatever machine Reed had that kept the door to the Negative Zone open."
Eternals such as Ikaris are not mere mutants. They were created by the Celestials from the earliest humans by jumpstarting their evolution and imbuing them with the ability to manipulate small amounts of cosmic energy. They're also almost immortal, and seemingly impervious to any sort of attack. Eternals bodies aren't physical in the sense that other beings are. The Eternals, through their control of cosmic energy and manipulation of matter, consciously hold their physical forms together on a molecular level. This means the only ways to kill an Eternal is to disperse their molecules across such a wide area that their consciousness cannot put themselves back together again, or to break their mental hold over their own form.
This means that Ikaris is almost certainly alive, but in the worst place possible. Even as a superpowered, almost immortal being, Ikaris is trapped in the Negative Zone with no real hope of escape. It doesn't matter how long he is there or how hard he fights, he will always be outnumbered. If he can't stay focused, without rest, potentially forever, then there is even a chance he could die of pure exhaustion. Hopefully this isn't the end for this version of Ikaris. Unfortunately, considering this is the universe of Earth X, hope isn't usually in high supply.