Sasuke could become a bit angry. He might see Sakura's ignoring as a sign of disrespect or a challenge to his pride. Given his prideful nature, he may not take it well and might even confront Sakura about it in a rather cold and haughty manner.
On the other hand, Sasuke may also start to reflect on his own behavior towards Sakura. Realizing that her ignoring might be a result of his own coldness all this time, he may start to consider changing his ways and showing a bit more warmth towards her, although it would be a very difficult and slow process for him.
He might be initially confused. Sasuke is not used to Sakura ignoring him as she has always been somewhat persistent in her attention towards him. So, he may be at a loss as to why she is suddenly acting this way.
One possible reason could be that Sakura has finally grown tired of Sasuke's aloof and cold behavior towards her. She might have realized that she has been constantly chasing after him while getting little in return, so she decides to ignore him as a form of self - preservation.
Sakura might initially be confused. She would probably wonder why Naruto is acting this way all of a sudden. For example, she might try to get his attention by calling his name a few times, but when he doesn't respond, she could be left feeling a bit bewildered.
She could be confused at first. She might not understand why Naruto is suddenly ignoring her, since they were friends before. So she might try to approach him to ask what's wrong.
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.
She might be initially heartbroken. Sakura, being in love with Sasuke, would surely be deeply affected when he neglects her. She could become withdrawn herself, losing some of her usual cheerfulness.
Sakura may initially be paralyzed by fear, but then her love for Sasuke and her own determination to survive could kick in. She might try to counter - attack in a non - lethal way, hoping to subdue Sasuke rather than harm him. She could also call out to their shared memories in an attempt to stop him from actually killing her.
Sakura could be a bit angry at first. She has grown and become more independent during his absence. When Sasuke shows regret, she may lash out, expressing all the pain and frustration she felt during his long absence, but deep down she still has feelings for him.
Sakura's character could develop by becoming more self - reliant. Ignoring Sasuke after the one night stand would force her to look within herself. She might start to value her own opinions and desires more. For example, she could become more assertive in the ninja community, speaking up in meetings and taking on leadership roles.
There are fanfics where Sasuke is a bit more reserved in his reaction. He may not show extreme emotions outwardly but instead, internally he's filled with a mixture of excitement and fear. He might start thinking about all the responsibilities that come with having a child and how his life as a ninja will need to change to accommodate this new addition to his family.
Well, it could be that Sakura finally realizes she's been chasing after Sasuke for too long and decides to move on. Maybe she starts focusing on her own life, her ninja skills, and her friendships more. And she just ignores Sasuke's actions that night as part of her newfound independence.