Well, it really depends on how the fanfic is written. If the fanfic focuses on Naruto's weaknesses and Danzo's preparedness, Danzo could potentially win. He has a lot of political power and experience. However, if it follows the general power scale of the Naruto universe, Naruto has a better chance. His positive energy and the power of friendship (a bit cheesy but true in Naruto's world) often help him overcome his opponents. Naruto also has the ability to quickly adapt to new situations, which would be a big plus against Danzo.
One possible plot twist could be that Danzo is actually being controlled by an even greater enemy. So, when Naruto is about to defeat him, he realizes that there's a bigger threat behind Danzo. Another could be that Danzo reveals a hidden power that he has been suppressing all along and suddenly becomes much stronger than Naruto expected.
He'll likely lose his power and influence in the village. Once Naruto reveals his secrets, the villagers won't trust him anymore. His actions might be put on trial, and he could be exiled from the village.
Maybe Naruto is put in a situation where he feels that Hiruzen's way of handling things is the best option. For instance, if there is a major crisis in the village that requires a more traditional and experienced approach, Naruto might choose to act like Hiruzen. Also, he could be influenced by the stories he has heard about Hiruzen and wants to fill his shoes in a way.
In a fanfiction of Hiruzen's daughter and Minato, perhaps Hiruzen's daughter is initially in awe of Minato's skills. Minato, on the other hand, is kind and respectful towards her. Their relationship could develop when they are paired up for a special mission. During the mission, they learn to trust each other completely and start to have feelings for one another. This could lead to a beautiful love story set in the world of ninjas.
One possible scenario in a 'Naruto Saves Hiruzen' fanfic could be that Naruto uses his newfound powers. Maybe he has mastered a new jutsu that allows him to turn back time briefly. He then uses this power to go back to the moment when Hiruzen is in danger. Naruto's quick thinking and his never - give - up attitude would be highlighted in such a fanfic.
Perhaps Naruto discovers a prophecy that Hiruzen will be in danger. So, he starts to train extra hard to be able to face whatever threat is coming. When the time comes, he uses his speed, which he has enhanced through rigorous training, to reach Hiruzen before the enemy can land a final blow.
One aspect that could be delved into is their different leadership styles. Hiruzen was more of a traditional leader, while Tsunade brought a new perspective. Fanfiction might show how they interacted regarding village policies and decision - making. For example, they could have had debates on how to handle the ninja academy or allocate resources.
One possible motive could be to gain control over Naruto's power. Since Naruto has the Nine - Tails within him, Danzo might want to use that power for his own political or military gains. He's always been power - hungry and sees Naruto as a tool to achieve his goals of making Konoha stronger in his own way, which might involve more underhanded and controlling methods.
It could also be a completely new character introduced into the fanfiction. A foreign ninja who was inspired by some of Danzo's ideas (not the bad ones) and comes to Konoha to take on the role of successor, bringing in new perspectives and ways of doing things.