It's hard to say for sure. If the fanfiction focuses on Hinata's growth, she could potentially defeat Pain through her own skills and some unexpected twists. But Naruto is also likely to be a major factor, so it could be a combined effort of both of them that overcomes Pain.
In this fanfiction, Naruto might be extremely enraged seeing Hinata in danger against Pain. Hinata, on the other hand, would likely show her newfound strength and determination. Maybe she'd manage to land a few surprise attacks on Pain before Naruto fully jumps into the fray.
Well, the Naruto vs Pain fight in the original series is epic. Fanfiction allows fans to explore different scenarios and what - ifs. Maybe they want to see different character developments during that intense battle.
There are many out there. A really good one might focus on the emotional reactions of Team Minato. For example, Minato might be proud of Naruto's strength and how he overcomes Pain. Kakashi could be in awe at Naruto's new techniques. Their reactions can enhance the overall viewing experience in the fanfiction.
The Konoha 12 would likely be in shock. They've seen Naruto grow, but this fight against Pain is on a whole new level. Some, like Shikamaru, would immediately start analyzing the battle strategies. Sakura might be worried sick about Naruto's safety, while Kiba could be cheering Naruto on loudly, impressed by his power.
The plot should be engaging. It could add new twists to the Naruto vs Pain battle. Maybe introduce some new jutsus or strategies that make the fight even more exciting. Also, good fanfictions in this category usually have a good balance between action and the emotional aspects of the characters.
The outcome in this fanfiction could be a draw. Naruto and Hinata would put up a great fight against Pain. Naruto would be all fired up, using his Rasengan and other ninjutsu. Hinata would be there, protecting Naruto's blind spots with her gentle fist techniques. But Pain is no pushover. His ability to control gravity and rain down destruction could keep Naruto and Hinata at bay, leading to a situation where neither side can fully defeat the other.
One of the most dramatic moments could be when Naruto first takes a really hard hit from Pain. The Konoha 12 would gasp in horror, and Sakura might even try to run out to help. Another moment could be when Naruto taps into a new level of power. The expressions of shock and awe on the Konoha 12's faces would be quite something.
In the original Naruto vs Pain fight, there were many unanswered questions. Fanfiction tries to answer those. For example, what if Naruto had more help? Or what if Pain had different motives? This makes it appealing to fans who want to explore these ideas.
You can try looking on popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). They usually have a wide range of Naruto - related fanfictions, and you should be able to find some with the 'Team Minato Watches Naruto vs Pain' concept.