Anti Sasusaku fanfic focuses on going against the Sasusaku relationship. So, while regular Sasusaku fanfic might show the growth and love between Sasuke and Sakura, anti ones would show the opposite. For example, they could show Sasuke constantly rejecting Sakura or having a negative view of her.
If Sakura dies in a fanfic, it could have a huge impact on the whole Naruto -verse within that story. Her friends like Naruto would be deeply affected. Naruto might feel like he failed to protect her, just as he felt about other losses in his life. And for the medical ninja community in the fanfic, her death could be a big blow as she was a talented medic.
A fanfic could show Sakura sacrificing herself to save Sasuke. This would be a very emotional and heroic end for her. Sasuke would then have to live with the guilt and the memory of her selfless act.
Yes, there are. You can find many on popular fanfic websites. These fanfics usually focus on the adventures, friendship and the start of the relationship between Sasuke and Sakura during their genin days.
One common theme is the strengthening of the Sasusaku relationship. The pregnancy often serves as a catalyst for Sasuke to become more involved and affectionate towards Sakura.
One popular 'bully Sasusaku fanfic' is 'A Change of Heart'. It shows an interesting dynamic where Sasuke initially bullies Sakura but then things start to change as they grow up.
Conflict is also a big theme. The love triangle creates a lot of conflict, not only between the three characters involved but also within their respective social circles. Friends might take sides, and there could be family interference as well, all of which add layers of drama to the story. For instance, if the third character is from a powerful family, they might use their influence to try and win over Sakura, causing a rift between Sasuke and Sakura at first.
It could be Orochimaru. He's always been interested in Sasuke and might see kidnapping Sakura as a way to manipulate Sasuke. He could use Sakura as a guinea pig for his experiments or as a bargaining chip to get Sasuke to come to him.
Well, one possibility could be that it's a dark fanfic where an enemy of Sakura kidnaps her to get to Sasuke. Maybe they want to use her as bait to lure Sasuke into a trap. Since Sasusaku is a popular pairing, the kidnapper might think that Sasuke would do anything to save Sakura.