One possibility could be that they are being mind - controlled. Maybe an enemy has found a way to manipulate them into attacking their own village. They might be used as pawns to create chaos in Konoha.
Sasuke would likely be very conflicted. He has a deep bond with Naruto, and he would not want to fight him, but he also has loyalty to Konoha. He might try to reason with Naruto first before taking any aggressive action.
It would be a huge blow to Konoha. Naruto is a hero in the village, and his departure would leave a big leadership void. The villagers would also lose a great source of inspiration. Hinata is from a respected clan, and her leaving would also have an impact on the clan's standing in the village. Morale among the ninjas might drop as they see two important figures leave.
They could leave because of a prophecy. Some ancient prophecy might state that they need to leave Konoha to fulfill a greater destiny elsewhere. So they trust in this prophecy and leave their home.
The village would have to rely more on other ninjas. Younger generations like Boruto and his friends would have to step up earlier. This could lead to a different kind of character development for them, as they are forced to take on more responsibilities without Naruto and Hinata's guidance.
One possible reason could be to seek a new life away from the politics and pressures of Konoha. Maybe they feel restricted by the village's rules and expectations. Another reason might be for a personal adventure. They could be in search of something that Konoha can't offer, like a new type of ninja training or a mysterious power source. Also, it could be related to protecting their family. If they sense some kind of threat to their family within Konoha, they might choose to leave to keep them safe.
From a security perspective, Konoha would be weaker. Naruto is a very powerful ninja, and Hinata is no slouch either. Their skills and abilities would be missed. Enemies might see this as an opportunity to attack Konoha. Also, Naruto has been a symbol of hope for the village. His departure could lead to a decrease in morale among the villagers. They might start to feel less secure and more pessimistic about the future.
Economically, there could be some impact as well. Naruto and Hinata are popular figures, and their presence in Konoha likely contributed to the local economy in some ways, such as through tourism (people coming to see the famous Naruto). Their departure might cause a dip in certain sectors that relied on their popularity, but it could also open up opportunities for new shinobi to rise and bring in new sources of income for the village.
In such a fanfiction, they might leave Konoha to start a new life in a peaceful place. Maybe they are tired of the shinobi life full of battles and politics in Konoha. They could find a small village by the sea and build a simple house there, living a quiet life away from the chaos.
Kiba would probably be shocked. He's Naruto's friend and also has a connection to Hinata. He might try to convince them to stay, saying things like Konoha needs them. But once he realizes they are determined, he would support them in his own way, like promising to visit them. As for Lee, he would see it as a very brave decision. He would be inspired by their courage to step out of their comfort zone and start a new life elsewhere.