In a darker fanfiction, Katniss could be assassinated. The Capitol, still angry about her rebellious acts, sends a highly skilled assassin. The assassin manages to infiltrate District 12 and kill her in her sleep. This would lead to a huge uprising as Katniss was seen as a symbol of hope for the districts.
Peeta would be heartbroken. He had strong feelings for Katniss, so her death would be a huge blow. He might become more determined to win the Games in her memory, to carry out whatever she might have wanted in the Games.
Well, it depends on the specific fanfiction. There are countless Hunger Games fanfictions out there. Some authors might choose to kill off Katniss to create a more dramatic or thought - provoking story. For example, they could make her sacrifice herself in a different way than in the original books, perhaps to save the whole of Panem in a more extreme situation.
One possible fanfiction could be about Katniss and Cato being forced to team up in an alternate version of the Hunger Games. Maybe they realize that the Capitol's control is the real enemy and start to work together to undermine the system from within the arena.
A fanfiction that stands out is 'The Everlark Chronicles'. It follows Katniss and Peeta's relationship from the start of the games all the way through their married life. It has some really heart - warming moments. 'Surviving the Aftermath' is also great. It focuses on how they deal with the political unrest in Panem after the games, and how their love for each other becomes a source of strength in those difficult times.
She could die from a mutt attack. The Capitol is known for creating those terrifying creatures. If, for example, a new type of mutt was specifically designed to target Katniss, she might not be able to fend them off and get killed.
One possible scenario in a fanfiction about Katniss' twin sister could be that she has a different set of skills. For example, while Katniss is known for her archery, the twin sister could be excellent at herbal medicine. This would add an interesting dynamic to the story as she could use her skills to help the tributes in different ways, perhaps by creating remedies for injuries or poisons. It could also change the relationship with Peeta, as the sister might have a different approach to the whole Hunger Games situation.
One great 'Katniss Peeta Hunger Games' fanfiction is 'Everlark's New Beginning'. It shows a post - Hunger Games world where Katniss and Peeta are rebuilding their lives together. It's full of sweet moments between them and really captures the essence of their relationship.
If Katniss never volunteered, the entire story dynamic would change. The other tribute selected might not have had her survival skills or determination.
It could have a huge impact. The tributes from Rue's district would probably be deeply moved. They might see Katniss as a hero for giving her life for Rue. And it could change the way the remaining tributes interact with each other. Maybe some would form alliances out of respect for Katniss's sacrifice, or some might be more hesitant to engage in violent acts against those who were close to Katniss.