His confidence could grow significantly. By being able to save two powerful ninjas, Naruto would prove to himself that he is capable of great things. He may start to believe more in his own abilities and take on more challenging tasks without hesitation. For example, he might be more willing to take on stronger opponents in future battles.
One possible plot could be that Sakura, being a skilled medic in the Naruto universe, comes across Zabuza and Haku who are severely injured. She decides to use her medical jutsu to save them. Maybe she's on a solo mission and her sense of morality makes her help them, despite them being former enemies. This could then lead to an interesting alliance or at least a mutual respect between them.
Well, in the original, Haku and Zabuza die. But in this fanfiction, Sakura's actions change that fate. This is a huge deviation as it completely alters the expected outcomes for those characters.
One interesting aspect could be the character development of Sakura. In the original series, she might not have had as much interaction with Haku and Zabuza. In the fanfiction, she could show new skills and a more assertive personality while saving them. For example, she might use her medical ninjutsu in creative ways to heal their wounds.
Sakura's character could develop in terms of her understanding of the grey areas in the ninja world. Saving Zabuza and Haku, who were once considered villains, might make her realize that not everything is black and white. She may become more open - minded and less judgmental.
One possible scenario in this fanfiction could be that Naruto discovers Haku and Kimimaro in a dire situation. Haku, with his ice techniques, and Kimimaro, with his powerful bone abilities, are perhaps being overpowered. Naruto, being the hero he is, jumps into the fray. He may convince them to change their ways and join him in Konoha, as he once did with Sasuke. This would not only show Naruto's growth as a ninja but also his ability to bring out the best in others.
In this fanfiction, Naruto might use his unique jutsus like the Shadow Clone Jutsu. He could arrive just in time to stop an enemy from killing Zabuza. Maybe Naruto realizes Zabuza's potential for redemption and decides to protect him.
The character development of Zabuza and Haku would be very different. Usually, they are portrayed as somewhat cold and isolated characters. But with Naruto around, they would be exposed to his warmth and positive attitude. Haku might develop more self - confidence and Zabuza could learn to trust others more. This would not only change their individual storylines but also how they interact with other characters in the long run.
One possibility is that Naruto could learn new combat techniques from Zabuza and Haku. Zabuza is a very skilled swordsman, and Haku has his unique ice-based jutsu. Naruto might pick up on some of their skills and incorporate them into his own fighting style, making him even more formidable in future battles.
Perhaps it's a group of mercenary ninjas. They've been hired by someone who has a grudge against Zabuza. They see Zabuza as an easy target when he's alone or vulnerable, but Naruto shows up to spoil their plan.