Found alive and alone in the King's CIC, still bargaining the launch codes for his own rescue, Nguyen is shot dead in the throat by Holden.
Admiral Nguyen survives, barricaded alone in the Agatha King's command information center, a large-caliber pistol shaking in his hand, while his ship fills with the protomolecule's improved zombies. When Holden fights his way in for the bioweapon launch-vehicle remote codes, Nguyen offers them only in exchange for a ride off the ship — the same bargain he'd tried with Avasarala. Holden refuses: give them up out of a scrap of humanity, or hand them over dead.
Nguyen clutches the terminal and the pistol, whitening his knuckles, and begins to insist 'You have to—' Holden shoots him in the throat. He dies clutching the codes, and Holden pries the hand terminal from beside his corpse — the last, small, frightened act of the man who launched a doomsday weapon at Mars to save his own failing career.
A squat, powerfully built Asian man in a UN admiral's uniform, a pistol trembling in one hand and a hand terminal clutched in the other, knuckles white with fear.
UN hawk who dies in his own CIC, executed by Holden while still bargaining the codes for his life.