He could fall behind his peers in terms of strength. If everyone else was training hard and he refused, he'd likely be at a disadvantage in battles or competitions.
His relationships with his mentors or those who were offering the training could be strained. They might see his refusal as disrespect or a lack of determination, which could lead to a rift between them. And without their support and guidance in the long run, Naruto could find himself in a difficult position in the ninja world.
He might become more determined to prove himself to Tsunade. This could make him train even harder within the village. He could also start to question Tsunade's decisions and try to find ways to convince her that he is ready for such a training trip in the future.
Perhaps he was tired of being pushed in a direction he didn't fully understand. He might have felt that the training was more about someone else's goals rather than his own. He wanted to find his own path to power without following a set training regime.
He would probably become very distrustful. After all, if your own parents betray you, it's hard to trust anyone else. He might isolate himself from others in the village, thinking that if his parents could turn on him, anyone could.
He would probably have to work really hard to repair the relationship. In fanfiction, Naruto's regret might mean he has to face Hinata's pain directly. Since Hinata has always been so devoted to Naruto, his cheating would be a huge shock. Naruto might try to be more open and honest about his feelings in the future. He could also face social consequences in the village. People might gossip about him and look at him differently. To fix things, he would need to show that he has truly changed and is committed to Hinata again.
He would gain new visual abilities. Naruto could now use the Sharingan's powers like predicting movements, copying jutsus more easily. But it might also come with some drawbacks. For example, the Sharingan consumes a lot of chakra, so Naruto would have to manage his energy better.
Naruto could end up getting lost, both literally and metaphorically. He might lose his way in the shinobi world, not having Minato's guidance. He could make wrong decisions about his training, alliances, etc.
In a fanfiction, if Naruto gets Shisui's Sharingan, he might face consequences in his training. He would need to learn how to control and master this new power, which could take time away from his normal training. This could potentially slow down his progress in other areas, like his Rasengan training or his control over the Nine - Tails' chakra. Also, his relationships with his non - Uchiha friends might be affected. They could feel left out or less important to Naruto now that he has this powerful Uchiha ability.
Asuma might provide combat - based training. He was a skilled fighter, so he could teach Naruto new jutsu and combat strategies. For example, his wind - style jutsu knowledge could be imparted to Naruto, enhancing Naruto's combat abilities.
Naruto would receive very diverse training. From Minato, he would learn about space - time ninjutsu. Minato was known for his Flying Thunder God Technique, and Naruto could inherit the knowledge to develop his own version. As for Tsunade, she would train him in close - combat skills. Naruto would learn how to throw powerful punches and use his chakra in a more brute - force way. Also, he'd learn about the importance of chakra control in medical ninjutsu from her.
Naruto would likely be extremely hurt emotionally. Tsunade is like a mother figure to him, and such a betrayal would shatter his trust. He might become more withdrawn and question his own worth.