The fourth and final season of Star Wars Rebels tied up a lot of loose ends and answered a lot of questions that had been posed over the years on the show, including the question of what happened to Ahsoka. For a long time, it seemed that Ahsoka must have died in the Season 2 finale that saw her dueling Darth Vader on Malachor. Sure, Ahsoka looked like she was alive and well enough to descend down into the Sith temple at the end of that finale, but there was no saying how she could have possibly survived when she logically wouldn't have stood a chance against Darth Vader himself in a duel. Season 4 revealed that there was a way for Ahsoka to have survived the otherwise devastating events of the Season 2 finale, and it has everything to do with the Force.
In the "World Between Worlds" episode of Star Wars Rebels, Ezra gained entrance into the Jedi temple on Lothal through a Force portal and discovered himself in a place where he had the potential to impact the past as well as the present and future, if the voices were anything to go by. Given the opportunity to stop Ahsoka from dying in her duel with Vader, Ezra yanked her to safety in the world between worlds, leaving Vader in the collapsing temple on Malachor alone. Star Wars Rebels showrunner Dave Filoni spoke with CinemaBlend about Ezra, Ahsoka, and the world between worlds, saying this:
The Jedi temple on Lothal was a mystery for a long time, and up until the moment the painting opened to reveal the portal, it was anybody's guess as to whether the secret within was a ship or a holocron or some other kind of artifact that could have been useful to Ezra and Co. in the aftermath of Kanan's death. The "world between worlds" idea came about when Dave Filoni began considering sending Ezra into an in-between place similar to Narnia in C.S. Lewis' Chronicles of Narnia series. The in-between place on Rebels was finally accessible to Ezra after he spent years opening himself up to the possibilities of the Force, largely with the help of Kanan.
This plane of existence was unprecedented enough in Star Wars canon that it could work perfectly to yank Ahsoka out of the moment that would have seen her demise, but precedented enough that fans wouldn't call shenanigans en masse. We didn't really have to suspend our disbelief any more than usual to enjoy Ahsoka's return and how it presented a connection back to the Mortis arc of The Clone Wars. That wouldn't have been the case if Ahsoka just dropped into the series finale and revealed that she'd hitched a ride off Malachor 20 minutes after the end of the Season 2 finale. In fact, her return opened a potential new frontier for the Star Wars universe to explore, on TV, in movies, or in other mediums.
Dave Filoni went on in our chat to explain why Ahsoka's return was important for Ezra at that point in his stories:
Despite having an unexpected part to play in the Rebels epilogue, Kanan died a full arc before the series actually wrapped up. Dave Filoni explained why the show killed Kanan relatively early in the second half of the season (and revealed some nods to Hera's big bombshell from the very end of the finale), and we now know that Ahsoka's return shortly after Kanan's death meant that Ezra was able to learn his last big lesson with the help of other mentor. Given how Ahsoka and Ezra worked together during their brief adventure in the world between worlds, is it any wonder that she agreed to come find him when they parted ways and she returned to Malachor?
Star Wars Rebels ended its fourth and final season with Ezra alive, but in parts unknown. The good news for him (and for fans who like the imagine the next leg of the characters' adventures) is that Sabine and Ahsoka were ready to set forth on a journey to find him and bring him home. He'll have a lot to catch up on, what with the existence of Jacen, the twist of fate for Kallus with Zeb, and perhaps even the heroics of Luke Skywalker. We can only guess at this point if Ezra and other Rebels characters will appear in Star Wars Resistance or the currently untitled live-action show. Ahsoka will be back when The Clone Wars finally returns with new episodes that will reveal the impact of Rebels.