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.
In a more complex scenario, Sasuke seeing Sakura kiss could be a turning point in their relationship within the fanfic's universe. If it's out of the blue for him, he could become angry or confused. He might question Sakura's loyalty or his own assumptions about their bond. It could also lead to him distancing himself from her, or conversely, finally realizing his true feelings and trying to win her back.
Sakura would probably be initially very angry. She has strong feelings for Sasuke, but kidnapping is a very extreme act. So she would likely fight back, using her medical ninjutsu skills and combat abilities to try and escape.
A third group of fans might simply ignore it. They are so set on the original story and the positive portrayal of Sasuke and Sakura's relationship that they don't want to engage with any fanfic that goes against that. They might consider it a disrespect to the original creators' intentions for the characters.
He could initially be in disbelief. However, as the reality sinks in, Sasuke would start to show his softer side. He might be more attentive to Sakura's needs, like making sure she eats well and rests. He would also start thinking about how to train their child to be a strong ninja in the future, while also wanting to give the child a more peaceful life than he had.
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.
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.
Sasuke would likely be initially shocked. He's a man who has been through a lot and is used to a life of solitude and danger. But then, a sense of protectiveness would kick in. He'd become more vigilant about the safety of Sakura and their unborn child. He might also start to think about how to be a better father than his own was, in some ways, trying to break the cycle of his family's past.
Sakura might be heartbroken at first. She has always been in love with Sasuke and to find out he's cheating would shatter her world. She could become withdrawn and focus more on her medical ninjutsu as a way to cope.
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.