Sasuke might initially be shocked. He has always seen Sakura as someone connected to Konoha, so her leaving would be unexpected. He could be concerned about her safety, especially if she leaves without proper preparation or protection.
This type of fanfiction concept is really out of the ordinary. Naruto's character is built on his values of friendship, loyalty, and his dream of becoming Hokage. Killing Sasuke would mean betraying all of that. However, in a fanfiction, the author might be exploring the 'what - if' scenario. For example, what if Sasuke's actions against Konoha were so heinous that Naruto felt he had no choice? But still, it's a far - fetched and very different view from the original Naruto we know.
One possible fanfiction could be that Sasuke returns to Konoha after a long mission. Sakura, who has been longing for his return, discovers she is pregnant. This news brings a mix of joy and worry. The village of Konoha is also excited as it means a new generation is coming. Sasuke might initially be shocked but then becomes determined to protect his family and the village.
Perhaps they are forced to leave due to false accusations or being framed for something they didn't do. This could create a situation where they feel they have no choice but to leave Konoha in order to clear their names and also protect the village from the real threats that might be lurking in the shadows.
Naruto might initially be in denial. He's so used to having Sakura around and believing that they have a future together. So when she leaves for Sasuke, he might think it's just a temporary thing or that she's been influenced by something or someone. But as time passes and he realizes it's real, he would be deeply hurt. He might also start to question his own self - worth, thinking that he wasn't good enough for Sakura. And he might even try to win her back at first, but then slowly come to accept the situation and focus on his other responsibilities like being a ninja and protecting the village.
In some fanfictions, Sakura may be determined to find Sasuke and bring him back. She could set out on her own journey, facing various challenges along the way, and growing both as a person and as a ninja in the process of trying to reunite with him.
Sakura's reaction would depend on how the author writes her character development. If she's become more confident in herself, she might approach Sasuke with a more assertive attitude. She could tell him that she's not the same girl he left behind. However, she'd still have that underlying love for him. She might also be worried about how the village will accept Sasuke's return and how it will affect her standing in Konoha. So her reaction would be a complex blend of personal feelings and concerns for the village.
One common theme is unrequited love. Often, Sakura has deep feelings for Sasuke which are shown through the symbol of sakura leaves. Another theme is redemption. The sakura leaves can represent new beginnings and Sasuke's journey towards redemption. For example, Sakura might use the beauty of the sakura leaves to remind Sasuke of the good in his life.
One possible reason could be Sasuke's pursuit of power. In many fanfictions, his thirst for greater strength might lead him to leave Sakura behind as he embarks on a solo journey to train in more dangerous and secluded places. He may feel that his goals are too dangerous for her to be involved with.
She may initially be angry. Sakura is a proud and strong character. She could confront Sasuke and Ino, demanding an explanation. After that, she might decide to become even stronger, both in her ninja skills and her emotional resilience, to show Sasuke what he's missing.