Only being buried in the secret passage could explain why they couldn't find him. However, Su Qing suspected that Qiu Yongkang would not die so easily.
Su Qing led her troops to chase after Qiu Yongkang, while Xiao Zeyu led his troops to wipe out all the armed forces in the Northern Barbarian Kingdom. Now that the Northern Barbarian Kingdom had been subdued, they needed to leave a portion of the Xiao Family Army to manage it. Xiao Zeyu thought of Jiang Laoqi. He had the courage and resourcefulness to be the Northern Barbarian Kingdom's City Lord. This could be considered a benefit that Xiao Zeyu had brought to his brothers.