I think the last "shot" was purely dramatic license for the story...it allows the "resolution" to convey the sacrifice...and it creates an "irony" based on Krennic's location.
One reason why I like to also read the books is the character's insights that is mainly lost in the screenplay.
Here is an excerpt from "Rogue One: A Star Wars Story" novel, an account of the last minute of Krennic's life.
Irony, yes, but Krennic wouldn't want it any other way.
“It was Wilhuff Tarkin who had commandeered his battle station. Tarkin alone would have the arrogance. Tarkin alone would have the spite to loom over Scarif and threaten the wellspring of all his own triumphs.
The Death Star’s focusing dish glittered with emerald light. Krennic’s fury built in key with the station’s energies and sought purpose, an outlet, a target. But Krennic’s body was ruined. His enemies were far from him. He had no one to command and no one to master, no one to sway into sharing his vision for the future or the Empire or his personal aggrandizement.
My father’s revenge.
Krennic was doomed, then, though it galled him to admit it. Yet while he might die at Tarkin’s hands, he would die in the fires of his creation. The Death Star would endure. He licked blood and spittle from his lips and imagined world after world consumed by his station’s power. Even the Emperor would not leave such a mark on the galaxy. The Death Star, his Death Star, would alter star systems and civilizations, be remembered a thousand generations after Tarkin had been erased from history.
And while Tarkin did live? He would know that every victory he eked out would be due to Krennic’s work. He would fumble his way through battle after battle, not truly understanding the weapon he wielded, until his arrogance destroyed him.
He built a flaw in the Death Star.
The focusing dish glowed brighter.
Krennic squeezed his eyes shut and used the last glimmerings of his mind to see the station as it was meant to be seen: to stand on the overbridge of his behemoth creation; listen to the reactor’s muffled roar turn to a shriek; feel the tremors in the deck plating turn violent as the kyber core exerted its strength. Jyn Erso had given her life to steal the Death Star schematics, but those schematics were etched in his heart.
You’ll never win.
He would die not on Scarif, but inside the Death Star.
And as he envisioned the cataclysmic energies building within the vast station, he saw it—a detail he had overlooked and forgotten, some trivial adjustment of Galen’s: a single exhaust port leading from a narrow trench down and down, down kilometers of blackness, past conduits and hatches and radiation plating, down and down— —and into the main reactor.
The primary weapon of the Death Star battle station fired.
Orson Krennic, advanced weapons research director and father of the Death Star, died alone on Scarif, screaming in fury at Galen Erso, at Jyn Erso, at Wilhuff Tarkin, and at all the galaxy.”
Excerpt From: Freed, Alexander. “Rogue One: A Star Wars Story.” Penguin Publishing Group, 2016-12-13T11:07:05Z. iBooks.
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