In the novel, the mockingbirds (Tom, Boo, and Dolphus) either lose their fight (Tom), or must retreat into hiding in order to fight another day (Boo and Dolphus). None of them can defeat the blue jays (Bob, the lynch mob, the courts) openly, legally. After all, Atticus takes on the Tom Robinson case knowing he will lose, but he fights for justice for the sake of his children (and to convince that one juror, Mr. Cunningham, to change his racial attitudes). The fight for justice is a losing battle now, soon to be won later.
Also, the fight for justice is generational. Since the novel is written during the Jim Crow era (1930s), Atticus' generation is fighting the battle for justice that Jem and Scout's generation will later cash in on (Civil Rights era). The narrator, now an adult lawyer like her father, is in the Civil Rights Era looking back on the Jim Crow Era with nostalgia, naivete, and some contempt.
The fight for justice was a fight lost to the town's black people. When Tom's case went to court it was not just about Tom Robinson. He was the person whose life was on the line, but he was also a representation of the way that black people were treated in the south and by the judicial system.
The glimmer of hope for change was the fact that one juror held out to actually debate the issue. He was a Cunningham as the previous editor stated.
Boo was still not fully justified because if everything had gone to trial he would not have fared any better than Tom Robinson had most likely. If there were a real winner, I would only say that it was the fact that Boo had ended Mr. Ewell's life. Justice was served by Mr. Ewell's death. He had raped and beaten his daughter, placed the blame on an innocent man and allowed him to die as an indirect result of his lies, and attacked the children.