Although things might seem set in stone for Arrow, especially with the death of a major character on the series, things that happen on another DC show could change everything.
In The Flash season finale, Barry Allen travels back in time and finally saves his mother, which means that the entire universe changes. That universe is also shared by those on The CW's other DC-related shows, including Arrow.
Actor Stephen Amell, who plays Green Arrow on Arrow, recently admitted that next year's story arc for The Flash could also affect his show.
The Flash actor Grant Gustin recently confirmed that its season three arc would cover the Flashpoint plot from the comic books. Flashpoint was one of the largest story arcs in the DC universe back in 2011 and affected nearly every hero in that universe, including Green Arrow. That plot had The Flash trapped in an alternate world where everything was different: Wonder Woman and Aquaman battled each other, Bruce Wayne's father was Batman and The Flash's mother was still alive.
According to Amell, that means that things could change for the TV version of Green Arrow, too. The actor mentioned the Flashpoint plot in his Facebook Live chat, calling the story arc "really cool." When a fan asked whether the story would affect Arrow, Amell's answer was simple: "Don't know; certainly could."
That's not necessarily a confirmation that Arrow will see some major changes when it returns for its next season, but considering how troubled its past few seasons were, a reset for the show could exactly be the shot in the arm it needs to make it better. It would also give the show a chance to redeem itself after killing off Black Canary, a move that angered many of the show's fans. She could still exist in the Flashpoint universe.
Things will definitely change for The Flash, though: in the season finale, Barry saved his mother and then began to fade away. With the first episode of the third season called "Flashpoint," it's likely that things will look and feel completely different next season.
Flashpoint could also solve a problem with Supergirl that previously had The Flash and Supergirl from alternate universes. With Supergirl now on The CW, and a major crossover event planned for all of The CW's superhero shows, the Flashpoint story could bring Barry and Kara together again in a way that makes sense.
Both Arrow and The Flash return to The CW this fall.