One possible reason in the fanfic could be her disillusionment with the Jedi Council. Maybe she saw too many of their political games and felt they were straying from the true Jedi path. For example, she might have witnessed them making decisions based on power rather than justice.
She could leave because of a personal revelation. In some fanfics, Ahsoka might discover a hidden aspect of the Force that the Jedi Order doesn't accept. This could make her feel like an outcast and prompt her to leave in search of a more inclusive understanding of the Force.
In such a story, the Jedi reader might find themselves on an adventure with Ahsoka. They could face the challenges of the Star Wars universe together, like fighting against the Sith or other dark side forces. Maybe they'll travel to different planets and encounter various alien species along the way.
In some fanfictions, when Anakin leaves with Ahsoka, they might go on a journey to find a lost Jedi artifact. This could lead them to unexplored planets and encounters with new species.
One possible reason could be disillusionment. In some crossovers, she might see the Jedi Order's flaws more clearly when exposed to different cultures or ideologies from the crossover elements. For example, if it's a crossover with a more individualistic society, she may start to question the Jedi's collectivist approach.
A disillusioned Jedi Knight. Maybe they've seen too much of the Order's bureaucracy and feel that the Jedi have lost their way. They might then be swayed by an outside force, like a Sith Lord, who offers a different vision.
In Star Wars Jedi: Fallen Order, the story is centered around Cal Kestis. He's on the run from the Empire that's hunting down the remaining Jedi. As he travels across different planets, he discovers secrets about the Jedi and his own past. He meets new allies and foes. Cal has to master his lightsaber skills and Force abilities anew to survive and bring back hope for the Jedi in a galaxy dominated by the dark side of the Empire.
Her departure could create a power vacuum in certain areas. Since she was a powerful Jedi, there might be regions she was protecting that now become vulnerable to the dark side or other threats.
Well, it might continue Cal's journey in exploring more of the Force mysteries. Maybe he'll face new and more powerful enemies, like some ancient Sith lords. He could also travel to new planets to find hidden Jedi knowledge.
Well, in a Star Wars fanfic, Ahsoka and the Son could have a very intense interaction. The Son represents the dark side, so Ahsoka, being a Jedi - ish figure, would likely be in conflict with him. She might try to resist his dark influence and fight against his malevolent plans. Maybe she'd initially be deceived by his charm, but then realize his true nature and engage in a battle of wills and lightsaber combat.
One idea could be exploring Ahsoka's immediate reaction during Order 66. Maybe she's in the middle of a mission with some clones she trusts, and suddenly they turn on her. It could show her struggle to survive while also trying to figure out what's wrong with her comrades. Another plot could involve Ahsoka finding other Jedi who managed to escape Order 66 and them teaming up to figure out how to deal with this new threat from the clones and the Sith behind it.
Well, a great plot might involve Ahsoka traveling through time. Maybe she gets sent back to the days of the Old Republic and has to interact with the great Jedi Masters of that era. She could learn new forms of lightsaber combat or ancient Jedi wisdom that she then brings back to her own time to use against a new enemy. Also, she could face a moral dilemma where she has to choose between following the traditional Jedi Code or her own instincts when dealing with a new type of enemy that the Code doesn't quite cover.