If Luke never left, Obi - Wan's legacy might not have been carried out as he hoped. Luke was meant to be the new hope for the Jedi. Other Rebellion soldiers would miss out on the inspiration that Luke provided. Lando Calrissian might not have joined the fight in the same way without Luke's influence. And the Ewoks might not have had their moment of helping the Rebellion if Luke wasn't there to be part of that final battle on Endor.
If Luke never left, it would change a great deal. He was so important in uniting different groups within the Rebellion. His absence from the Jedi training might mean that the knowledge of the Force would be less widespread in the Rebellion. Also, his story of facing Vader was a turning point. Without that, Vader might not have had the change of heart that he did, and the fate of the galaxy could have been much darker.
It could change the way the Rebellion is fought. Ezra's knowledge of certain parts of the galaxy and his connections could be added to Luke's growing influence. This might lead to a more coordinated effort against the Empire. For example, Ezra could inform Luke about some hidden Imperial bases that he discovered during his adventures in the Rebels.
Luke runs away to a desolate planet. There, he tries to hide from the Empire and his own past. He lives in solitude, meditating on the Force and trying to come to terms with his inner turmoil. However, he soon realizes that he can't escape his destiny forever.
Their meeting could have a huge impact on the galaxy. They could form an alliance that unites different factions. Since Ahsoka has connections to various groups and Luke is a symbol of hope for the Rebellion, together they could bring more planets under the banner of peace and freedom.
The other characters would be greatly affected. Her death could shatter the Rebel Alliance's morale. Leia was a symbol of hope and leadership. Without her, there could be internal power struggles. Some might try to fill her shoes but fail, leading to chaos. It could also change the way the galaxy views the fight against the Empire. Her diplomatic skills were important, and without her, the Alliance might struggle to form new alliances or keep the ones they have.
The impact of Luke being sick in a fanfiction could be huge. For example, it could change the dynamics of his relationships. If he's sick, Leia might become more protective, and Han could be more on edge about their safety without Luke at full strength. It could also slow down any planned missions or battles as they wait for him to recover.
One possible motive could be extreme guilt. In the Star Wars universe, Luke has faced many challenges and made some tough decisions. If he were to make a huge mistake, like accidentally leading the dark side to a major victory, the guilt might be overwhelming. He's a character with a strong sense of justice and responsibility, and such a blunder could make him feel unworthy of living.
Luke would probably be in awe of Kanan's skills as a Jedi, despite his different training. He might learn some new tricks from Kanan. With Ezra, he could be like a mentor, guiding him further in the ways of the Force. And with Hera, he'd respect her leadership and might offer his own strategic insights based on his experiences fighting the Empire.
Luke would likely develop a deeper understanding of the Jedi's roots. This could make him more traditional in his approach to the Force, or it could make him question some of the Jedi teachings he learned in his own time. Leia, on the other hand, might develop a more global view of the galaxy. Instead of just focusing on the Rebellion, she could see how different factions interacted throughout history, which would shape her leadership style in new ways. For instance, if she saw how the Sith influenced events from the shadows in the past, she would be more vigilant in her own time.
As they go on adventures together, their bond would strengthen. They could face a great enemy like a powerful dark side user. In the heat of battle, they would rely on each other and start to trust more deeply. Ahsoka might see some of Anakin in Luke, which would make her more protective of him, and Luke would see Ahsoka as a wise mentor figure.