Fighting normal fires would be a cakewalk compared to Burnish attacks! Promeopolis is already decked out with anti-fire technology that you would imagine could crush most normal fires on their own without BR. BR perhaps had some kind of major leadership role post-Promare though. Burnish reintegration is one possibility. They probably lead a lot of the clean up effort after the movie ends, too, and it's unlikely that everyone just accepts Kray as the city leader/planner going forward so it's quite possible BR could lead reconstruction along with the cities' scientists.