One consequence could be Naruto's emotional turmoil. He would be completely shattered as his mother, who he probably idolizes, has turned against him. This could lead to him doubting himself and his place in the world.
It could also split the village. Some people might side with Kushina, believing that she has a good reason for her actions, while others would stand by Naruto. This would create a great divide and lead to internal conflict within the village.
On a more personal level for Naruto, it could change his view of family forever. He might become more closed - off and less trusting, not just of Kushina but of others as well. And if Kushina is a powerful figure in the village, her betrayal could also make Naruto an outcast as people might be afraid to associate with him for fear of getting on Kushina's bad side.
One consequence could be Naruto's emotional breakdown. Since Kushina is his mother, her betrayal would be a huge blow to him psychologically. He might start to doubt himself and his place in the world.
One possible plot could be that Kushina is somehow influenced by an evil force. This force makes her believe false things about Naruto, like he's a threat to the village in the future. So, she betrays him by revealing his secrets or trying to harm him. Maybe she spreads lies about him which turns the villagers against Naruto even more.
One consequence could be a shift in Naruto's character development. Having his mother back might make him more at ease and less driven by his past loneliness. It could also change his relationship with other characters. For example, his bond with his father figure, like Iruka or Jiraiya, might not be as strong as it was when he was motherless. Another consequence could be in the political aspect of the ninja world. Kushina was an Uzumaki, and her return could strengthen the Uzumaki clan's position and influence, which might cause some unrest among other clans who fear the growing power of the Uzumakis.
In some really complex fanfic plots, there could be a prophecy or some sort of ancient power play involved. Suppose there is a prophecy that Naruto will bring great destruction in the future, and Kushina is made aware of it through some dark magic or secret organization. She might think that betraying Naruto now is the only way to save the village and the world, even though it goes against her motherly instincts. This would be a very convoluted and interesting take on the idea of her betrayal.
At first, Naruto would be shocked and confused. His world view would be shattered. But then, he would draw on his inner strength. He has overcome so many hardships before. He might feel a deep sadness, but also a sense of resolve. He would still believe in the power of love and friendship, and use that to face Kushina's betrayal. He could also use this experience to grow even stronger and more determined to prove himself and his beliefs.
One consequence could be that Naruto becomes an outcast in a different way. In the original, he was an outcast because of the Nine - Tails, but here, it could be because of his abandonment. He might not have the same dreams of becoming Hokage. Instead, he could be more focused on survival.
On a more personal level, they could face internal guilt. As Naruto grows up and achieves great things on his own despite their neglect, Minato and Kushina may realize what they've missed out on. This realization could cause them a great deal of internal turmoil and regret for not being there for their son when he needed them.
Naruto would likely be deeply hurt, not just physically but also emotionally. He has always idolized his mother, so an attack from her would be a huge blow to his psyche. His trust in family and those close to him could be severely damaged.
The first consequence could be a breakdown in the village's unity. Naruto is seen as a hero in Konoha, and if he turns against it, many of his supporters might be confused or even follow his lead. This could lead to internal strife within the village.
It could also be related to some hidden family secrets or prophecies. Maybe there was a prophecy that Naruto would bring great destruction in the future and Kushina, believing in it, thought she had to stop him before it was too late. This would be a very complex and heart - wrenching betrayal if it was based on such a false premonition.