Sasuke might become more isolated. Without Sakura's presence, he could sink deeper into his brooding and revenge - seeking state. He may start to question if he has truly lost something valuable, which could either harden his resolve further or make him more self - reflective in a negative way.
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.
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.
Sakura might be heartbroken. She's been in love with Sasuke for so long. She could initially go into denial, thinking it's just a temporary thing. Then she might get angry and vow to prove herself to Sasuke, perhaps by becoming an even stronger ninja.
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.
One reason could be that Naruto realizes his feelings for someone else and doesn't want to mislead Sakura. In some fanfictions, Naruto might discover that his true love is Hinata and so he steps away from Sakura to pursue a relationship with Hinata without causing any confusion for Sakura.
One possible reason could be her long - standing and deep - rooted love for Sasuke. Since childhood, she has had strong feelings for him. Maybe in this fanfiction, she realizes that her feelings for Sasuke are unshakable and that she can't continue to be with Naruto while having such intense feelings for another.