Kakashi would be deeply concerned. Given his relationship with Sasuke, he'd feel a strong sense of duty to save him. He'd use his extensive network of contacts within the ninja world to try and find out where Sasuke has been taken. He might also reflect on his past training with Sasuke and how he can use that knowledge to anticipate the kidnappers' moves. He'd be ready to face any danger or obstacle in his path to rescue Sasuke. And he'd be constantly thinking about Sasuke's safety and well - being during the whole process.
Sasuke would probably be very guarded at first. He's not used to dealing with something so innocent and vulnerable. He might be suspicious of the baby's presence and think it's some sort of trap.
Sakura would be heartbroken. She'd likely spend hours upon hours by Naruto's side, trying to jog his memory with stories of their adventures together. She might even get a bit overbearing in her attempts. Sasuke, who has his own complex relationship with Naruto, would be conflicted. He'd see Naruto's forgetfulness as a sign of weakness at first but then realize the importance of their bond. Kakashi, being the experienced leader, would start by observing Naruto carefully to see exactly how much he has forgotten and then start a systematic process of helping him remember.
Sasuke would be furious. He's always been protective of Naruto in his own way. He would immediately start looking for her, using all his skills and resources. He might even go on a rampage if he thought Naruto was in serious danger.
On the other hand, Sasuke could be very stoic about it on the surface but internally be in turmoil. He might start to analyze his own actions and whether he had missed any signs from Sakura. He could also be the type to immediately start thinking of ways to win Sakura back if he realizes he can't stand the thought of her with someone else.
Sasuke might be initially surprised. He is used to the Sakura from his past, so seeing a different, more mature future Sakura could catch him off guard.
I think young Sasuke would have a very intense reaction. He was so consumed by his hatred for Itachi at that young age. A Sasuke vs Itachi fanfiction would be like a trigger for him. He would be eager to see how the fictional fight is portrayed. If Sasuke in the fanfiction is shown as strong, it might fuel his own ego and make him strive even harder to become powerful. However, if the fanfiction shows Itachi as superior, it could enrage him. He might feel that it undermines his own goal of defeating Itachi and he might even want to find the writer to correct their 'wrong' view.
The villagers would be shocked. Naruto is like a hero to them, and the idea of him joining a group like Team Hebi, which has some anti - village vibes, would be hard to accept. His friends like Sakura would be heartbroken. She has always counted on Naruto to be by her side in Konoha. Kakashi, as Naruto's mentor, would be very concerned. He would try to talk Naruto out of it, explaining the importance of his place in the village. Shikamaru, being the strategic thinker, would see it as a potential threat to the village's stability and might even come up with a plan to stop Naruto from leaving.
In some cases, Sasuke could be angry. He might see Naruto's request as a sign of weakness or as Naruto giving up too easily. He could lash out at Naruto, telling him to fight instead of asking for death. However, he would still be deeply troubled by the request and would probably struggle with it for a long time, constantly thinking about whether or not he should consider it.
Sasuke could react very angrily. He might lash out at Sakura verbally, asking her how she could do such a thing. He has always been a bit of a hot - headed character, and this situation would likely trigger his temper.