In the fanfiction, the abuser may have to go through some form of rehabilitation or counseling if the law requires it. Hopper could ensure that the abuser is held accountable and has to make amends. If the abuser has a family, they might also face problems within the family as a result of their actions being exposed. And if there are other victims out there, they may come forward once the abuser is exposed, which would further compound the abuser's problems.
The abuser might face social ostracism. Once Hopper reveals the abuse, the community would likely turn against the abuser. People would stop associating with the abuser, and it could lead to the abuser losing their job or status in the town. Also, there could be legal consequences like having to pay fines or go to jail depending on the severity of the abuse and the laws in place.
The abuser might find themselves ostracized by the whole demigod community. Word would spread about what they did, and no one would want to be associated with them. Also, they could be targeted by other protective figures in Percy's life, not just Poseidon. The gods and goddesses who have some connection to Percy or just have a sense of justice would make sure the abuser pays for their actions. They could be cursed to have a series of misfortunes befall them, like always being in the wrong place at the wrong time and facing various dangerous situations.
In the fanfiction, the abuser might be ostracized by the society. People would start to question his motives and actions. His influence in the wizarding world, whether it's in business or politics, would decline rapidly. The abuser might also have to face the wrath of some of the more powerful and just characters in the story. They could use their influence to make sure the abuser is held accountable for his actions.
They might face magical punishment. For example, they could have their magic restricted or be sent to Azkaban if it's a really bad case. McGonagall would not tolerate such behavior and would push for the strictest punishment.
The abuser could face magical justice. In the wizarding world, there are probably spells or enchantments that can be used to punish wrongdoers. James Potter might use his connections to ensure the abuser is dealt with severely, like being sent to Azkaban or having their magic restricted.
The abuser might face the wrath of the champions. They could be reported to the authorities in the wizarding world.
The abuser might face the wrath of the DA. They could be ostracized within the wizarding community. The DA members could use their influence to make sure the abuser is held accountable for their actions.
He might be very angry. Hopper is a protective character. He could immediately start to plan how to get Billy out of the abusive situation and confront the abuser.
The abuser could face public shame. Rita's articles could expose their actions to the entire wizarding community.
In the fanfiction world, the abusers may find themselves ostracized by the wizarding community once Viktor reveals what they've done. If Viktor has friends or allies in high places, they could ensure that the abusers are held accountable for their actions. There could also be legal consequences within the wizarding laws if the abuse is of a certain nature. For example, if it involves dark magic or illegal forms of coercion, the abusers could be sent to Azkaban or face other forms of severe punishment.
If the champions decide to take matters into their own hands, they could use magic to teach the abusers a lesson. For example, they could jinx the abusers so that they are unable to harm Harry again. However, if they report to the school, the abusers might face a formal hearing. Depending on the severity of the abuse, they could be banned from certain areas of the school, lose house points, or even be permanently removed from Hogwarts. There could also be social consequences, like being shunned by other students.