The stabbing of Clary can completely shift the direction of the fanfiction. It can create alliances that were not there before. Other characters might put aside their differences to find out who stabbed Clary and why. It can also introduce new elements to the story, like a new weapon or a new type of magic that is needed to heal Clary. Plus, it can heighten the tension between different groups, such as the Downworlders and the Shadowhunters, if there is suspicion among them regarding the stabbing.
The other characters would likely be in shock. Jace, for example, might be filled with rage and a desperate need for revenge. He would probably blame himself for not being there to protect Clary. Alec might be more practical, immediately trying to find a way to heal Clary. Isabelle would be a mix of worry and anger, angry at whoever dared to harm her friend. Their reactions would also depend on the context of the stabbing within the fanfiction.
Simon might be in a bit of a panic. Since he's her friend and also not as used to the dangerous situations as the other Shadowhunters. He'd try to do whatever he can to help, like getting help from more experienced Shadowhunters or trying to comfort Clary while she's in pain.
Alec might also come to her rescue. As a skilled Shadowhunter, he has a strong sense of duty. Plus, he's part of Clary's group, and he wouldn't stand by and let a fellow Shadowhunter be attacked by a demon.
The theme of future and responsibility is also often explored. Clary has to think about not only her own future but also the future of the baby. This includes things like where she'll live, how she'll raise the child, and how it will impact her goals and dreams. For example, if she was in the middle of some important mission or study, the pregnancy will force her to reevaluate all those aspects of her life.
Well, she might be rescued by her friends. In many fanfictions, her Shadowhunter comrades would come to her aid, using their unique skills to fend off the attackers.
Another character who has a personal vendetta against Clary or her family. For example, a jealous rival or someone who blames her family for past misfortunes. This would add a layer of drama and personal conflict to the fanfiction.
I'm not sure specifically as there could be many different interpretations in such a fanfiction. It might involve a character named Rito facing a stabbing incident, perhaps in a battle, a crime scene, or a situation of betrayal.
On the other hand, there could be a glimmer of hope in their relationship. Maybe through the shared experience of the pregnancy, they start to see the good in each other. Clary might see a side of Sebastian that she never knew existed, and Sebastian might start to have real feelings for Clary and the baby, leading to a more complex and evolving relationship.