Another character could come to his rescue. For instance, Sasuke might show up at the crucial moment. Despite their complex relationship, Sasuke still values Naruto as a friend or rival. He intervenes and stops Sakura from killing Naruto. Or perhaps Kakashi, Naruto's teacher, arrives in time. He uses his Sharingan or some other jutsu to neutralize Sakura's attack and save Naruto.
In the fanfiction, Naruto could also survive due to some unforeseen plot twist. Maybe there is a hidden power or ability within Naruto that is only activated when he is in extreme danger. This power could reverse the situation, not only saving his life but also making Sakura come to her senses. It could also be that the fanfiction's world has some kind of magical protection or prophecy that ensures Naruto's survival in this near - death encounter.
One possible reason could be a misunderstanding. Maybe Sakura is under the influence of some dark magic or mind - control in the fanfiction, which makes her lose her rational judgment and attack Naruto. Another reason might be a strong emotional outburst. For example, if she discovers something she believes Naruto has done wrong, but in fact it's a misinformation, and her anger gets the better of her, leading to her almost killing Naruto.
Naruto could try to talk her out of it. He is a firm believer in the power of friendship and words. So, he would likely use his words to try and break whatever spell or wrong idea is in Sakura's head that made her want to kill him.
Another possibility in this fanfiction concept could be that Sakura was under some sort of mind control. An enemy might have manipulated her into attacking Naruto. This would create a very tragic and complex storyline, as it would involve the undoing of all the positive bonds they had developed over the years.
He might survive through his own sheer willpower. Naruto has always been a tenacious character. So, even when left for dead, his determination to live and achieve his dreams could keep him alive against all odds.
He survives through his strong will. Naruto has an unwavering determination that refuses to be broken by Orochimaru's experiments. His inner strength and the chakra of the Nine - Tails within him might also play a role in withstanding the physical and mental torture of the experiments.
In some fanfics, he might be saved by his latent magic power that suddenly bursts out when he is in extreme danger. For example, it could create a protective shield to fend off the Dursleys' attacks.
He uses his ninja skills, of course. His shadow clone jutsu can be very useful for scouting and distraction. And his Rasengan is a powerful attack that can fend off many threats.
Naruto might be very forgiving right away. He has always had a big heart and cared deeply for Sakura, so he could just accept the apology with a big grin and say it's all in the past.
Naruto could also feel a deep sense of hurt. After all, he has been through a lot with Sakura. In the face of her betrayal, he might start to question his own judgment of people. However, being Naruto, he would not give up easily. He might try to find a way to redeem Sakura or at least make her see the error of her ways. He would draw on his own experiences of being ostracized in the past and use that to try to understand her actions and find a solution.
Sometimes, in fanfiction, Naruto stands up to Sakura when it comes to her attitude towards Sasuke. Sakura might be blindly following Sasuke's every move, and Naruto, having a more objective view of Sasuke, could confront Sakura. He would tell her that she should value herself more and not just revolve her life around Sasuke. Naruto has his own understanding of friendship and loyalty, and he would use that to make Sakura see things differently.