It could mean that the members of Team 7 in the Naruto universe are fans of Naruto fanfiction. Maybe they enjoy reading stories written by fans about their own adventures or different scenarios in the Naruto world.
It might be that 'team 7 loves sakura fanfiction' simply refers to fan - created stories where Team 7 has a particular fondness for Sakura. This could be in various ways. It could be a story where they protect her at all costs because of their love for her. Or it could be a story that focuses on how Sakura is the heart of Team 7, and the other members' love for her is what keeps the team together in the fictional world of the fanfiction.
The concept is popular because it allows fans to fill in the gaps in the original story. The anime and manga may not fully explore all aspects of Kakashi's feelings for Team 7. Fanfiction gives the opportunity to go deeper into their relationships. For example, how does Kakashi really feel when Sasuke leaves the village? What does he do behind the scenes to support Naruto's growth? These are the kinds of things that fans love to write about and read in fanfiction.
The scenario where Team 8 saves Team 7 instead would be quite interesting. It could introduce new conflicts and resolutions, and potentially reveal hidden strengths of Team 8 that weren't previously showcased.
You can try some popular fanfiction websites like FanFiction.net or Archive of Our Own (AO3). Just use the search terms 'team 7 loves sakura' on these platforms and you should be able to find relevant fanfictions.
Kurenai might be a good sensei for Naruto's different team. Her expertise in genjutsu would be valuable. She could help the team develop their skills in this area, especially if the new team members have some potential in genjutsu. Kurenai is also very perceptive, which would be great for guiding Naruto and his new teammates through difficult situations.
Sakura would be heartbroken. She'd likely spend hours upon hours by Naruto's side, trying to jog his memory with stories of their adventures together. She might even get a bit overbearing in her attempts. Sasuke, who has his own complex relationship with Naruto, would be conflicted. He'd see Naruto's forgetfulness as a sign of weakness at first but then realize the importance of their bond. Kakashi, being the experienced leader, would start by observing Naruto carefully to see exactly how much he has forgotten and then start a systematic process of helping him remember.
Well, it could make the team more protective. Sasuke might feel a stronger sense of rivalry as he wants to be the best in the team even with Naruto in this new role. Sakura would probably be very motherly, always fussing over Naruto. And Kakashi would have to adjust his teaching methods to accommodate Naruto's new situation.
It could also be due to a major disagreement with Kakashi. Maybe Naruto has a different vision for how they should operate as a team or a particular mission that goes against his values, causing him to leave.