Well, there could be an epic battle. Maybe the Justice League is facing a powerful enemy and Barry Allen, with his super - speed, arrives just in time to turn the tide. He could use his speed to disrupt the enemy's attacks and create opportunities for the other members of the Justice League to strike.
Perhaps they start off as rivals at first. Bruce might be a bit suspicious of Barry's powers and his more light - hearted approach. But as they get to know each other better, they realize they can learn a great deal from one another. Barry could teach Bruce to loosen up a bit, while Bruce could show Barry how to be more strategic in his superhero work.
The Reverse - Flash could be a great main villain. He has a long - standing feud with Barry Allen and his presence would force Barry to team up with the Justice League. The Reverse - Flash's ability to manipulate time in his own way could pose a huge threat not just to Barry but also to the entire Justice League.
If Barry kidnapped Supergirl in fanfiction, it could be a really interesting plot twist. Maybe Barry has been affected by some sort of red kryptonite - like substance that makes him act out of character. This would lead to a conflict between the Flash and Supergirl's friends and allies. They would be confused as to why Barry would do such a thing.
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.
In certain comic versions, Barry Allen is indeed identified as Jewish. This aspect is sometimes incorporated into his character background and story arcs.