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The war was over...
With the Void Prince dead, most of the Royal Guards gone, the population of the Void Creatures culled in mere hundreds, and the main consciousness of the void sealed, the war was truly over. All that's left was the cleanup.
It's safe to say that the Void Creatures wouldn't be a problem again, and if they could help it, forever.
There had been casualties. That can't be avoided; it's war after all. However, the casualties on the side of the living beings were very minimal. A mass funeral and honoring took place for them, and the Border Patrol Office ensured that the bereaved families were compensated appropriately.
Regardless, this was an astounding victory for them. With the leading figures of the void disposed of, the void won't be a danger anymore. So much so that the gates can be left wide open with confidence, and the office could now set up branches into the void itself for more convenience.