The adoption would have a profound impact on the DC Universe. Firstly, in terms of storylines, there would be a whole new set of arcs centered around Bruce and Barry's relationship. For example, how Bruce helps Barry master his powers while also dealing with his own issues. Secondly, it could change the way the superhero community views family. If Bruce can successfully adopt and mentor Barry, it might inspire other heroes to take in proteges. And finally, it could affect the balance of power in the universe. With Barry having Bruce's support, he could become a more dominant force in battles, which might force villains to rethink their strategies and alliances.
It's hard to say for sure. Some parts of the story might be based on real events, but there could also be fictional elements added for dramatic effect.
Barry Allen's death in the comics is a complex situation. Sometimes he does die, but often there are plot twists and resurrections as part of the ongoing comic narrative. It all depends on the creative direction of the writers and the demands of the story at that time.