Well, perhaps it's a misunderstanding. Some villain may have tricked Sasuke into believing Sakura was a threat, so he ties her up. Later, he realizes his mistake and has to make amends. Or it could be a scenario in a parallel universe where the relationship between them is very different, and this kind of situation is normal for their strange new dynamic.
It could be a situation where Sasuke is trying to protect Sakura from herself. Sakura has been affected by some sort of dark magic or chakra, and Sasuke, having no other option at the moment, ties her up to prevent her from harming others or herself. As the story progresses, he then tries to find a way to reverse the effect on her.
One possible plotline could be that it's part of a training exercise gone wrong. Sasuke, in his overzealous attempt to train Sakura, ties her up to test her escape skills. Another could be that they are in a dangerous situation where Sasuke has to restrain Sakura to keep her safe from an unseen enemy. Maybe they are in a magical or cursed area where Sakura's movements need to be restricted for a while.
One possible plotline could be that Sakura is physically held by Sasuke against her will, and she struggles to break free while also dealing with her complex feelings for him. Maybe she's trying to understand his motives for holding her in such a way.
A possible plotline could be that they are both on a mission to rescue their kidnapped comrades. They have to work together, using their unique ninja skills. Female Sasuke with her lightning - fast attacks and Sakura with her super - strong punches.
In some fanfictions, it could be that Sakura is under a genjutsu (illusion technique). The genjutsu makes her act in ways that seem like she is cheating on Sasuke. She doesn't realize what she is doing until it's almost too late, and Sasuke has to figure out what is really going on to save their relationship.
Perhaps Sasuke uses Sakura to get closer to some information. He might know that Sakura has connections or knowledge that can help him in his quest for revenge or for protecting the village. So he uses her in a strategic way while she is initially unaware of his motives. As the story progresses, their relationship could develop in complex ways.
Well, perhaps Sasuke has to leave the village again for some mission or his own personal vendetta. He doesn't explain his reasons fully to Sakura, and she feels abandoned once more, which makes her cry. In a different scenario, Sasuke might be in a battle where he has to make a tough decision that involves sacrificing something that Sakura holds dear. When she realizes what he's done, she's heartbroken and cries. Or it could be that Sasuke is training extremely hard and pushing himself to the limit. Sakura is worried about him, but when she tries to stop him, he dismisses her concerns harshly, reducing her to tears.
One possible plotline could be that they leave to seek a new form of power. Maybe they've discovered a threat that the Hidden Leaf isn't aware of, and they believe they can find a solution outside. Another could be that they're on a journey of self - discovery. Sakura has always been in Sasuke's shadow to some extent, and this could be her chance to truly find herself while being with him. Also, perhaps they leave due to some political unrest in Konoha that they don't want to be a part of.
One possible plotline could be that Sakura decides to raise the child on her own. She focuses on her medical ninjutsu to provide for the baby. Another could be that she tries to find Sasuke again to make him take responsibility. Maybe she faces challenges from the village as a single mother, but her friends support her through it all.
One possible plotline could be that Sasuke is under some sort of dark magic or mind control when he binds Sakura with snakes. Maybe an enemy has manipulated him into doing this as part of a larger scheme against the Hidden Leaf Village. And Sakura, being the strong - willed kunoichi she is, tries to break free and also reach out to the real Sasuke within his mind - controlled state.
A possible plotline could be that Sakura discovers she has a rare and dangerous pregnancy complication. Sasuke, initially shocked, vows to protect her and find a solution. He might go on a journey to find a rare herb or seek the help of a reclusive healer. Meanwhile, Sakura is in the village, trying to stay strong and use her medical skills to keep herself and the baby alive as long as possible.
One possible plotline could be Sasuke becoming increasingly possessive as Sakura's popularity or friendships grow. He might start to isolate her from others, thinking it's for her own good.