1. Ophelia: Ophelia, the daughter of Polonius, is driven to madness by Hamlet's rejection of her and the death of her father. She eventually drowns herself in a river. If Hamlet had not been killed, he might have been able to save Ophelia or prevent her from taking her own life.
2. Laertes: Laertes, the son of Polonius, seeks revenge against Hamlet for killing his father. He challenges Hamlet to a duel and poisons his sword, intending to kill him. However, Hamlet manages to turn the tables on Laertes and kills him with the poisoned sword. If Laertes had not been killed, he could have succeeded in his quest for revenge.
3. Claudius: Claudius, the King of Denmark, is the main antagonist of the play. He killed his brother, King Hamlet, in order to become king and married his widow, Gertrude. Hamlet plots to kill Claudius to avenge his father's death, but he is ultimately unsuccessful. If Hamlet had been able to kill Claudius, it would have changed the course of the play and prevented the tragic events that followed.
4. Gertrude: Gertrude, Hamlet's mother, is married to Claudius after the death of her first husband, King Hamlet. She is aware of Claudius's crime but chooses to remain silent. Hamlet is disgusted by his mother's actions and contemplates killing her, but he ultimately hesitates. If Hamlet had killed Gertrude, it would have further complicated his relationship with Claudius and deepened his sense of guilt.
5. Rosencrantz and Guildenstern: Rosencrantz and Guildenstern are Hamlet's childhood friends who are sent by Claudius to spy on him. They are eventually executed by Claudius for their failure to carry out their mission. If Hamlet had been killed, Rosencrantz and Guildenstern might have been spared.