He might lose his sense of self. Tartarus is a place of great despair and horror. The constant exposure to such a negative environment could break his spirit. His friends might think he's dead and move on, which would also add to the tragedy when he eventually gets out, if he does.
One possible consequence could be that he becomes even more powerful in a dark way. Tartarus is full of dangerous and ancient forces. Staying there might expose him to unique and powerful magics that change him. For example, he could gain new combat skills or the ability to control certain Tartarus - born entities.
His relationship with the gods could change drastically. The gods might see him as a liability if he stays in Tartarus for too long. They could fear that he'll bring some of Tartarus's chaos back to the upper world. On the other hand, some gods might try to rescue him for their own purposes, like using his potential power for their own agendas.
He might face extreme physical challenges like battling powerful monsters on his own. In Tartarus, there are many dangerous creatures that could be a huge threat.
Perhaps he could make an alliance with some of the less hostile creatures in Tartarus. There might be beings who are also tired of the chaos and want to help Percy in exchange for something, like a promise to free them from Tartarus if he ever gets the chance. Percy is known for his charisma and ability to make friends, even in the most unlikely situations.
There are several possible reasons. Firstly, for the sake of drama. It makes for a very intense and emotional story when a beloved character like Percy dies. Secondly, it could be to explore the after - effects on the other characters. How would Annabeth cope? How would the Camp Half - Blood react? Also, it might be a way to show the unforgiving nature of Tartarus.
Perhaps a plot where Percy forms an unlikely alliance with some of the more neutral or even hostile creatures in Tartarus. He could use his charm and wits to convince them to help him in his struggle against the greater evils of that place. In this way, he learns more about the complex hierarchy and politics within Tartarus.
One consequence could be that the fanfiction community might feel less connected to the character. If Percy doesn't seem to interact with or acknowledge the fan - created stories, fans might feel like their creativity isn't being recognized. For example, they might be less motivated to write more stories about him.
It could lead to a breakdown in the demigod community. Percy is kind of a hero figure, and if he doesn't care, it might demoralize other demigods. They might start to question their own purpose and the importance of their roles. Also, it could make Camp Half - Blood more vulnerable to attacks as Percy is a strong fighter.
A third plotline could be Percy's search for a powerful artifact or knowledge in Tartarus that could help him in his future battles or save his friends. Along the way, he discovers secrets about the origin of the gods or the true nature of Tartarus itself, which changes his understanding of the world he thought he knew.
In some fanfictions, Percy's torture in Tartarus could be part of a grander scheme. For example, an enemy on the surface world has made a deal with the forces of Tartarus to weaken Percy. As he endures the torture, he gradually uncovers the conspiracy and tries to find a way to not only escape but also stop those who sent him there. His friends, unaware of his situation at first, start to suspect something is wrong and embark on a quest to find out what happened to him and rescue him.
One possible character arc for Percy could be a journey from confusion to acceptance. At first, he may be completely bewildered by this new 'heir of Tartarus' status. He might resist it, but as the story progresses, he could come to accept it and find a way to use it for good. Another arc could be a fall - and - redemption arc. He could initially be corrupted by the power of Tartarus and turn against his friends, but then through some self - realization and the help of those who still believe in him, he could be redeemed.
One possible plot development could be Percy facing off against new and terrifying monsters that are unique to Tartarus. Maybe he discovers some long - lost secrets about the place that could change the way the demigods view Tartarus in general.