If Wakanda were to actually be decimated to the degree Hickman depicts, especially if it were still deprived of its wealth of Vibranium rendered inert to defeat Doom, Wakanda would be vulnerable to attack (not sure attack is right given the current state of its defenses, more like looting) to every nation that previously failed at invasion. Even neighboring countries which may never have attempted to invade Wakanda would be bolder for the former power's weakness.
As such, the only way I can imagine T'Challa rebuilding the Golden City is if the devastation did not extend to Wakanda's surrounding tribes and villages and T'Challa was able to recruit new staff, a new council, new defense forces, etc., from the followers of the Whie Gorilla cult, N'djaka village and others. Unfortunately, T'Challa is poorly positioned to garner the confidence of any dissidents given his culpability in the events that have resulted in Wakanda's demise.
My two cents,
Peace,
Mont
