One possible consequence is that the power balance in the ninja world is completely disrupted. With the Kyuubi's massive chakra and power running free, smaller villages might be constantly in fear of being attacked. Konoha, in particular, would have to find new ways to defend itself without relying on the fact that the Kyuubi is sealed within one of its shinobi.
If the Kyuubi isn't sealed in Naruto fanfiction, Naruto's character development would take a very different turn. He wouldn't have to go through the internal struggle of taming the Kyuubi's power within him. Instead, he might have to face the Kyuubi as an external enemy. This could lead to a more adversarial relationship between them, and Naruto would have to develop his skills in a different way to deal with this powerful being.
The presence of an unsealed Kyuubi would likely change the political landscape of the ninja world. Alliances might be formed differently. For example, villages that were once enemies might unite against the common threat of the Kyuubi. On the other hand, some might try to use the Kyuubi's power for their own gain. There could also be new types of ninja techniques and strategies developed specifically to deal with an unsealed and powerful Kyuubi.
Well, in fanfiction, the Naruto and Kyuubi fusion could lead to a change in how the ninja world views Naruto. He would be seen as an even greater threat or an even more powerful ally. For example, other villages might be more hesitant to engage in conflict with him. Also, his relationship with his friends could be affected. They might be in awe of his new power but also a bit worried about the Kyuubi's influence on him. And on a physical level, his appearance might change, perhaps taking on some of the Kyuubi's features, like his eyes or his hair color getting a more reddish tint.
Well, one reason could be that the author wants to explore an alternate universe. Maybe in this fanfiction's version of the Naruto world, the events leading to the sealing of the Kyuubi never occurred. It could be due to different political situations among the ninja villages, or perhaps a different chain of events that prevented the Kyuubi's attack on Konoha in the first place. So, without the attack, there was no need for the seal.
One consequence could be a huge power boost. Naruto would become extremely strong, which might change the power balance in the fanfiction world. Enemies would be more cautious of him, and allies might rely on him more. Another consequence could be the internal struggle. The Kyuubi has its own will, so Naruto might have to constantly fight to maintain control when it's summoned.
In some fanfictions, Kaguya being sealed might lead to new mysteries emerging. For example, there could be hidden secrets or powers that were associated with her that now start to surface. This could draw in new characters or lead to new adventures for the existing ones. Maybe some of Kaguya's leftover chakra starts to influence certain events or people in unexpected ways.
The balance of power in the Naruto universe of the fanfiction could be disrupted. If Bardock was a powerful force against some impending evil, his sealing could allow that evil to thrive. For example, if there was a powerful enemy that Bardock was meant to fight, with him sealed, the enemy could start to conquer and cause chaos more easily. Also, his friends or allies might start a quest to unseal him, which could lead to many adventures and encounters with other characters, both good and bad.
One possible consequence is that Naruto might lose control of his own actions. The Kyuubi is a powerful and often uncontrollable force. So, he could end up causing a great deal of destruction without meaning to. For example, he might attack his friends or allies in the heat of the moment as the Kyuubi's power overwhelms his own judgment.
One consequence could be that he becomes extremely powerful. His physical abilities like strength, speed, and endurance are enhanced. He can also use more powerful jutsus with the extra chakra boost from the Kyuubi.
One possible consequence could be a shift in the power dynamics in the Naruto universe. If Naruto frees the female Kyuubi, she might become an ally. This could change how battles are fought as she could bring her unique powers to help Naruto and his friends. For example, she might have different abilities compared to the regular Kyuubi, like more refined chakra control which she could teach Naruto.
In some fanfictions, when Naruto loses control of Kyuubi, other villages might see it as an opportunity to attack Konoha. They may think that with Naruto out of control, Konoha is in a weakened state. This could start a whole new arc of conflict where Konoha has to defend itself not only from Naruto's unleashed power but also from external threats.
In some fanfictions, the immediate consequence could be destruction. Buildings might be razed and many shinobi could be injured or killed. The village would be in chaos as they try to either contain Naruto or the Kyuubi's power. There could also be a shift in the power dynamics, with some seeing Naruto as a threat and others trying to find a way to calm him down and reseal the Kyuubi.