Some fanfictions might show Percy getting angry. He could feel betrayed, especially if he doesn't understand the reasons behind the breakup. He might lash out, either verbally or by going off on his own on some dangerous adventure to deal with his emotions.
He might be initially in shock. Percy has been through a lot with Annabeth, so being dumped would come as a huge blow. He could be speechless for a while, unable to process what has just happened.
Well, Percy is a complex character. His reaction could depend on how much he knew about the pregnancy before Annabeth left. If it was a complete surprise, he might be in denial for a while. He could also start to blame himself, thinking he had somehow failed her. And then he might eventually turn that pain into a determination to be a better person, whether or not he ever sees Annabeth again.
Another reason might be personal growth differences. As they grow, Percy and Annabeth may develop in different directions. Annabeth could become more focused on her academic and architectural pursuits in the fanfiction world, while Percy remains more centered on his demigod adventures. This divergence in their interests and life paths could cause Annabeth to feel that they no longer share the same connection and thus dump Percy.
Annabeth would be very shaken up. After the initial shock, she would assess the situation calmly. If Percy is unconscious, she would try to find a way to wake him up. She might talk to him, recalling their memories together, hoping it would reach him on some level. And she would be very protective of him while he's injured, not allowing any further harm to come to him. She would also feel guilty, thinking that if she were stronger or more careful, Percy wouldn't have had to protect her and get hurt in the first place.
Percy might be a bit flustered and embarrassed. He's protective of his relationship with Annabeth, so having Magnus walk in might make him feel like their privacy has been invaded. He could quickly try to shield Annabeth or just look really shocked.
She might be heartbroken at first. She could try to jog Percy's memory by showing him things that were important to them.
Annabeth could also be angry, not at Percy but at the situation or the forces that led to his death. She might vow revenge and start on a journey to find out who or what was responsible for Percy's sacrifice and make them pay. This could lead her into a whole new set of adventures and challenges as she tries to come to terms with her loss.
She'd probably be shocked at first. But then her face would light up with joy. After all, she and Percy have been through so much together.
Well, it depends on who is flirting with her in the fanfiction. If it's someone she doesn't like, she'll probably be dismissive and give cold responses. However, if it's someone she has a bit of an interest in, she could be coy and a bit shy while still maintaining her confident facade.
He could also become withdrawn and depressed. Percy and Annabeth have a very strong bond, and her death would leave a huge void in his life. He might isolate himself from his friends and family, lost in his grief and memories of her.
He would probably be shocked. Percy has always trusted Annabeth, so being stabbed by her would be completely unexpected. He might initially be unable to believe what's happening.