She might be shocked at first. Sakura has always known Naruto as someone who is very attached to Konoha. If his leaving is because of her, she could feel guilty. She might try to stop him, asking him why he's doing this and telling him that he doesn't have to go.
In the fanfic, Sakura could also be angry. She might see Naruto's leaving as a selfish act, especially if she doesn't return his feelings. She could feel that he is abandoning the village and his friends for something that she doesn't believe is worth it, and lash out at him before he goes.
Sakura could be confused. She may not fully understand the depth of Naruto's feelings for her that would lead him to leave Konoha. She might think that Naruto is overreacting and try to convince him that his place is in Konoha, with his friends and the village that he has always wanted to protect.
She may feel angry at first. Sakura is a strong - willed character. She might think that Naruto has made this decision without considering her feelings. In the fanfic, she could go on a rant about how he should have talked to her before making such a big decision.
She might be heartbroken. Sakura could initially be in shock and then fall into a deep sadness. She may blame herself for Naruto's leaving, thinking that she could have done something differently.
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.
She could be heartbroken. Sakura has always loved Sasuke deeply, so his leaving for Naruto would be a huge blow to her. She might initially be in denial, not believing that Sasuke would choose Naruto over her.
Sakura might be in shock at first. Unable to believe that Naruto, who has always been so strong - willed, could have ended his own life. As she processes it, she could become angry, not at Naruto but at herself and the situation that led to this tragic outcome.
Well, it could be that Naruto feels he doesn't fit in Konoha anymore. Maybe he's constantly being misjudged by the villagers despite his efforts to protect them. Also, if his relationship with Sakura is a big factor in his leaving, it might be that he can't bear to see her with someone else, like Sasuke perhaps, and decides to leave to avoid the heartache.
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.
In other fanfics, Naruto might try to understand Sakura's perspective. He's a very forgiving person, so he could give her the benefit of the doubt and try to figure out what made her act in a way that hurt him. He might think that she had her reasons and try to work through it with her.
Sakura might initially be confused. She has known Naruto for a long time and his sudden coldness would be unexpected. She may try to reach out to him to find out what's wrong.
She might be initially shocked and hurt. Sakura has always had Naruto as a constant in her life, so his sudden absence would be difficult to accept. She could become withdrawn and start to question her self - worth.