Imagine Harry returning with Warrington’s body, and the crowd realizes what’s happened, but Warrington’s parents don’t show up. There’s no one to mourn him, to cradle him in their arms and cry for their son. The Slytherins know why. His parents were Death Eaters, too.
Imagine Slytherins reaching out, asking for help from classmates from other houses. They’re terrified, truly terrified because the being their parents claimed would never hurt them because they’re pureblood, they realize that he does not care.
Imagine Slytherins in the 5th book sneaking off to join Dumbledore’s Army, to learn more about who Voldemort is without their parents acting as a filter.
Imagine the shock when they’re told what he’s really done.
Imagine that a few talented Slytherins went with Harry and the others into the Ministry of Magic. The others are a bit wary but they prove themselves as friends.
Imagine them being confronted by Lucius Malfoy in the the Hall of Prophecy, and when the Death Eaters descend, they know that any one of them could be their parents.
Imagine the shocked gasp of a Death Eater as they realize their own child, a pureblood, is standing defiantly with Harry Potter. They choke back a cry. They can’t let their child know that they were about to duel to the death.
Imagine a DA Slytherin facing off against their own Death Eater parent. That they make the decision to let their child defeat them, because in that moment, they realize that they love their child more than they fear Voldemort. They go down, mask unveiled, and the Slytherin kid has to be dragged from the fight before he gets killed.
Imagine Book 6 Slytherins getting more friendly and cooperative with the other houses. Two years of Voldemort terrorizing the muggle and Wizarding world, two years where their parents just up and leave some days, cringing from the pain in their arm, two years after the death of the first Slytherin pureblood, Cassius Warrington, killed by Voldemort’s right-hand man, and they’re slowly hitting the breaking point.
Imagine Slytherin kids keeping tabs on their parents, sending the information to Harry, who shares it with the Order of the Phoenix, and hoping that their parents won’t be killed.
Imagine Book 7 Slytherins low-key rebelling against the new oppressive Hogwarts staff.
Imagine the final siege on Hogwarts, where Slytherins stand proudly by their fellow houses, knowing full-well they could be fighting their own parents. Some Slytherins know their parents were in the fighting. They hope to find them first and sneak them away. Their fellow students understand. Professor McGonagall allows 7th Year Slytherin, Pansy Parkinson, to duel a death eater in her stead; her father is under that veil. She knows it.
Imagine the aftermath of the battle; every house suffered loses. Slytherin students crying over the deaths of friends they made in every house.
Imagine a Cassius Warrington statue made in his honor, the first Slytherin to fight and die nobly with Harry Potter, the boy who lived, in the face of ultimate evil. He was a true Slytherin, and it’s in his name that Slytherin children and their families have cut all ties with the Death Eaters, denounced Voldemort, and are finally living in peace.