u/ConstantStatistician

I've seen some confusion over this, so I thought I'd explain what happened. It's true: Raleigh was written as dying when Uprising came out. This was directly described in Mako's flashback in chapter 3 of the Ascension prequel novel. He died from radiation poisoning shortly after his exposure to the Anteverse. Mako got sick too, but she survived because she was in the Anteverse for less time than him.

>She and Raleigh – and her adoptive father Stacker Pentecost, and others – they had beaten the enemy, killed the Kaiju, and destroyed the portal by which those monsters entered the world. And everything was fine. The world was saved.

>In ten years, nothing had come out of the Breach.

>But they had taken Raleigh anyway, hadn’t they?

>Both of them had been poisoned by the radiation from the Anteverse; she remembered days in bed, blood transfusions, highly experimental treatments for both of them. Still they had been together in a sense, going through the same thing, victims of the same affliction. She drew strength from him and he from her.

>But then she started to get better.

>Raleigh did not.

>The scientists called it the throat, a sort of interdimensional tube through which the Kaiju emerged into their world. She and Raleigh had gone down the throat, and Raleigh had ejected her before rigging the atomic core of their Jaeger – Gipsy Danger – to melt down.

>Once she was out, he descended further. As she rode, unconscious, in her escape pod, he and Gipsy drifted out the other end of the throat, into the Anteverse itself. Raleigh used Gipsy’s nuclear vortex turbine to propel the Jaeger back into the throat, and then ejected himself, seconds ahead of the detonation. He’d spent a handful of heartbeats in the Anteverse, but those were seconds longer than she had been there. He tried to describe to her the things that he saw there, but they didn’t make that much sense, even to him.

>Poisoned by the radiation of another world, he fought, as he always fought.

>She was holding his hand when he died. She heard his last words. He had been asleep, but when he opened his eyes, the old brightness was still there. He was still there.

>“Mako,” he whispered, squeezing her hand. “All you have to do is fall. Anyone can fall.”

>And then he wasn’t there. Not in a rush, not in battle, but in a quiet moment that did not seem nearly big enough for the weight of his person. Raleigh had been cheated. She had been cheated – of Raleigh, of her adoptive father, of her life as a pilot.

This is reiterated a few times in the Uprising novelization and implied in the film itself when Jake Pentecost mentioned Raleigh's name next to Stacker and Mako's, who were both dead by then.

Of course, this was indeed later retconned in season 2 of The Black, where Raleigh is said to have survived and his whereabouts are unknown. He's definitely shown to be alive in the Final Breach comic, where he's one of the main characters along with Jake.

So that's Raleigh's character. He was originally killed off but had his death retconned and was brought back by later materials.