Leia would be devastated. She and Luke have a strong bond as siblings. His death would not only be a personal loss but also make her question the future of the Resistance or the New Republic. She might become more reckless in her fight against the dark side, driven by grief and a need for vengeance.
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.
Kanan's death in fanfiction makes the remaining characters grow in different ways. For Chopper, it could mean being more protective of the others. Zeb might become more solemn. The whole group might also find new sources of inspiration from Kanan's sacrifice. They may remember his teachings and use them to face greater challenges. His death can be a catalyst for character development, pushing them to be stronger and more united in their cause.
Hera would be heartbroken. Sabine was like a daughter to her. Hera would likely become more protective of the remaining crew members. She might also be more hesitant in future missions, but she would also know that Sabine would have wanted them to keep fighting. So, she would try to balance her grief with the need to continue the Rebellion, and she would make sure Sabine's story and sacrifice were remembered among the Rebels.
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.
The Jedi Council would also feel the impact. Ahsoka was a young and promising Jedi. Her death would make them re - evaluate their training methods and their role in the Clone Wars. There could be internal conflicts within the council as they debate over what went wrong and how to prevent such losses in the future.
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 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.
It could make them more determined. For example, his comrades might become more resolute in their fight against the enemy, vowing to win in Jerome's memory.
For Kakashi, it would be like losing his student all over again. He has trained Naruto and seen his growth. His death would make Kakashi question his own role as a teacher and mentor. He might become more withdrawn and blame himself for not being able to prevent Naruto's suicide.
Prince Eric would be devastated. He fell in love with Ariel for her beauty, both inside and out. Her death would leave him heartbroken, and he might become a recluse, spending his days mourning by the sea. He could also become a bit of a crusader, trying to do things in Ariel's memory, like cleaning up the ocean or protecting mermaids.