Judging by the fact that Du Busi led the evacuation of the Heavenly Soul Empire's nobility, and that the Tianhun Emperor burned himself to death within the city—a ruler dying alongside his state—preparations must have been made quite some time in advance.
Continuing to rely on Du Busi to hold down Tiandou City, keeping a Limit Douluo trapped there like that, was certainly not what the Tianhun Emperor would have wanted.
To prevent this, he had even gone so far as to brazenly set fire to himself, asking only that Du Busi evacuate with the royal family of the Heavenly Soul Empire, plotting a restoration of the nation another day and freeing up Du Busi's immense power as a Limit Douluo.
Chapter 1026