Naruto could be in a state of shock at first. But then his determination would kick in. He'd recall all the times Sakura has been there for him and the team. Knowing that Sasuke has kidnapped her, he'd feel a sense of betrayal too, since Sasuke was once their teammate. He'd likely gather his friends and start planning a rescue mission right away.
Well, Naruto might be furious. He's always been protective of Sakura. He'd probably drop everything he's doing and go after Sasuke to rescue Sakura. Naruto has a strong sense of justice and loyalty, especially towards his friends. And Sakura is one of his closest friends, so he won't stand by and let her be in danger.
Sakura would probably be initially shocked and angry. She has always cared about Sasuke, and this betrayal would hit her hard. But she is also a strong - willed ninja. So, she would quickly gather her wits and start looking for ways to escape. She might try to use her knowledge of Sasuke's fighting style against him if she gets the chance.
Sakura might initially be very angry. She has her own strength and pride, and being kidnapped by Sasuke, someone she once cared for deeply, would be a huge blow to her self - esteem. She could try to fight back immediately, using her medical ninjutsu skills and combat training to attempt an escape.
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.
He may also choose to defend himself without really fighting back. Naruto values Sakura as a friend and teammate, so he would be reluctant to harm her. He might just try to dodge her attacks and keep talking to her, hoping to snap her out of it.
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.
Sasuke would likely be enraged. Naruto is his rival and also, in a way, his friend. He would immediately set out to find Naruto and confront Itachi. Sasuke has a strong sense of pride and would not let his brother get away with this.
She would probably be very angry at first. Naruto is a headstrong character, and being kidnapped against her will would make her furious. She'd likely try to fight back immediately, using whatever skills she has at her disposal.
Sakura would be over the moon. She would blush deeply and look at Sasuke with so much love in her eyes. She might be at a loss for words for a moment, but then she would find her voice and tell Sasuke that she has been waiting for this moment her whole life. She would also feel a sense of pride that Sasuke has chosen her, after all they have been through. And she would immediately start thinking about how to share the good news with their friends, especially Naruto, who has been like a brother to her and has also been a part of their journey.
Sakura might be initially frustrated. She's used to Sasuke being in control, so seeing him drunk could be a bit of a shock. But then she'd probably feel a sense of protectiveness and try to sober him up.
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.