Harry might be initially in shock. He can't believe Ginny would leave him and their child. He could become withdrawn, not really knowing how to deal with this new situation.
In this type of fanfiction, it could be that Harry has some unresolved issues from his past relationship with Cho. He sees Ginny as a distraction from dealing with those. But as time goes on, he can't ignore the pull he still feels towards Cho. He may leave Ginny when he realizes that he can't move forward in his life without exploring what could have been with Cho again.
The first consequence could be the breakdown of his friendship with Ron. Since Ron is Ginny's brother, he would likely be very angry at Harry for hurting his sister. Another consequence might be the division within the wizarding community. Fans of Harry and Ginny as a couple would be disappointed, and there could be a lot of speculation and gossip.
One possible reason in such a fanfiction could be a magical bond that forms between Harry and Draco unexpectedly. This bond might be stronger than his relationship with Ginny. It could be a result of a shared magical experience or a prophecy that ties them together in a way that makes Harry question his feelings for Ginny and ultimately choose Draco.
One possible reason could be miscommunication. Maybe they had a big fight over how to raise their child and Ginny, feeling unheard, decided to leave. Another reason might be external pressure. For example, if some dark forces were targeting their family again and Ginny thought leaving would keep Harry and the child safer. Or perhaps Ginny had some personal issues she couldn't deal with while being in the family, like feeling she lost her own identity in the relationship.
Ginny's character could develop in several ways. She may initially be heartbroken and feel lost without Harry. But as the pregnancy progresses, she could find an inner strength. She might become more protective, not just of her unborn child but also of her own feelings. She could also become more empathetic towards other single mothers in the wizarding world. This experience could make her a more complex and well - rounded character, no longer just the girl who was in love with Harry but a strong woman facing a difficult situation.
One possible reason could be a misunderstanding. Maybe there was a miscommunication between them, like Ginny thought Harry was still too preoccupied with his past traumas and not fully committed to their relationship. Another reason might be external pressure. In some fanfictions, there could be outside forces, such as dark wizards threatening Ginny and she leaves Harry to protect him.
For Harry, he might experience a sense of relief and new - found happiness with Ginny. He's been through so much, and Ginny represents a more stable and loving relationship compared to the complex dynamic with Draco. Ginny, on the other hand, would be overjoyed to finally have Harry fully committed to her. For Draco, it would be a huge blow. He might feel rejected and angry, especially since his relationship with Harry was always so competitive.
Ginny would likely be heartbroken. She's a strong character but she loves Harry deeply. She might start to question herself and what she did wrong. Cho, on the other hand, would be surprised but also happy. She may have still had feelings for Harry all along. Harry himself would be conflicted at first, feeling guilty for leaving Ginny but also excited about the possibility with Cho.
Obviously, Harry would be an important character even though he leaves. His actions before leaving and potential return would greatly affect the story. Also, the Weasley family, especially Ginny's mother Molly. Molly would probably be very involved, offering her motherly advice and support. Ron and Hermione might also be involved. Ron as Ginny's brother would surely have an opinion and Hermione could be there for Ginny as a friend.