I also highly doubt that Gabranth is dead. Taking a look at the Field Notes on Noah, it says the following:
Bold for emphasis, but the body is identified as being Gabranth. However, it's also worth taking a look at the Field Notes on Dabog II:Later, the body and armor of the ill-fated Gabranth would be discovered by the resistance, though he was not immediately identified as such—in part because the burns were so severe that his face could scarcely be recognized, and in part because so few had seen the face under the mask in the first place. Still, in the end, the identity of the corpse was confirmed, and news of the death of Noah van Gabranth spread across the land.
Sicinius developed the technology to extract a person's memory and implant them in the body of a hypertuned soldier that he has shown great skill at aesthetically modifying. My bet is that Sicinius created a stronger body for Gabranth by taking a hypertuned soldier, modified it to look like the original Gabranth, and then implanted all of Gabranth's memories in it. It lets Gabranth fake his death perfectly by torching the old body, and as an added benefit, gives him a stronger body which he may have needed given the theories about him suffering from the same disease that killed his father, and his final cutscene where he talks about not having much time left. I figure he'll be back as the figure influencing Princess Ashe behind the scenes.To speak in terms that you might understand, I devised a technique that allowed the extraction of memories from my dear test subject VIII, Dabog. Said memories could then be implanted into other Hrothgar captives, thereby allowing mass production of hypertuned soldiers. Brilliant, is it not? It was a breakthrough that would forever change the face of war as we knew it. Or rather, it should have...
I am admittedly something of a perfectionist─it was not enough to simply manufacture an assortment of hypertuned soldiers. They had to be perfect. Uniform... Which is why I may have made more than a few aesthetic modifications to ensure they all resembled the original Dabog. I can hear Valens now. “Why even bother!? All those damned animals look alike.” And he certainly isn't wrong─they all do bear an uncanny resemblance to one another. Nevertheless, it was a detail I refused to overlook. And I could scarcely wait to see the looks upon your comrades' faces when my soldiers took to the field.