Kakashi, as their sensei, would be disappointed. He would hope that they could resolve their differences maturely. He might offer some advice based on his own experiences in relationships, but ultimately it would be up to Itachi and Sakura to decide whether to take it or not.
The other members of their team or the village might have mixed reactions. Some might side with Sakura, understanding her point of view, while others might think she's being hasty or that they should try to preserve the relationship for the sake of the village's stability or their own friendship circle.
Shikamaru, being the more laid - back but perceptive friend, would likely be disappointed. He might see the signs that led to the divorce coming from a mile away but feel powerless to stop it. He would probably just sigh and say something like 'What a drag' while still being there for both Naruto and Hinata as a friend.
The Weasley family would be divided. Molly would be heartbroken as she always saw Hermione as part of the family. Some of the Weasley siblings might side with Ron out of loyalty, while others might understand Hermione's point of view. Ginny, for example, might be more empathetic towards Hermione as a fellow woman who has her own ambitions.
Sakura would probably be angry at herself for being captured. She's a proud ninja. So she would start looking for weaknesses in Itachi's hold on her. Maybe she would try to engage him in conversation to find out his motives, all the while formulating a plan to break free. She could also try to send out some sort of signal to her comrades if possible.
Naruto would be deeply saddened. He has always hoped for Sasuke and Sakura to be happy together. He might initially try to mediate and get them to work things out, believing that their relationship can be salvaged. He would remind them of the good times and how much they mean to each other.
Sakura would probably be initially terrified. She would try to use her medical ninjutsu skills to defend herself or at least slow Itachi down. If she realizes she can't overpower him physically, she might try to talk to him, asking him why he's doing this.
Iruka sensei would be very proud of Naruto. He has been like a father figure to Naruto, and seeing him get married to Sakura would make him feel like Naruto has truly grown up. As for the other villagers, most of them would be happy as Naruto is a hero. They would see Sakura as a great match for him, someone who can support him and also contribute to the village with her skills.
Sakura might initially be terrified. She would probably try to fight back using her combat skills and medical ninjutsu to defend herself. Since she is a strong - willed character, she won't go down without a fight.
She might be a bit confused at first. After all, Itachi has a very complex and somewhat dark past. But she could also grow to understand her father's perspective as she learns more about Itachi herself.
Sasuke would probably be very confused at first. He has spent so much time hating Itachi for what he did to the Uchiha clan. Seeing Naruto befriend Itachi would make him question his own long - held beliefs. He might initially be angry with Naruto for seemingly siding with his enemy.