We'll start with the more obvious - Severus Snape. I'm not here to say that he was such a small character with such a minor role that he should have died because of that, or that he was an awful character and all that shit. It's purely because his usefulness had frankly run its course. He played a substantial role as the one who basically infiltrated Voldemort's army and turned things around on themselves, due to some sort of insane but brilliant plan concocted by Dumbledore, all the while helping the heroes take down voldemort and his horcruxes, but the truth is, after all of that, after the war had already started, and after Harry, Ron and Hermione had already found and destroyed all but three of the horcruxes, what next? Only on his deathbed would he finally do something useful, and explain everything to Harry. Don't get me wrong, he was one of my absolute favourite characters in the series, his heroism knows no bounds, but the truth is that Voldemort was basically defeated, Lily died a long time ago, and Voldemort would have disposed of him anyway, so his part in the story was essentially over. It was going to happen anyway, due to Snape killing Dumbledore, and Voldemort's absolute stupidity got the better of Snape, but even on his deathbed, Snape's final act was to tell Harry everything - about how he himself is a horcrux, how Dumbledore asked him to murder him, and how he needed to sneak into Voldemort's army in the first place. And even then, even if Snape did survive the battle, at what point would he have been able to defect from Voldemort's army in the first place? He would have stood beside Voldemort, albeit unwillingly, and would have likely been killed by one of the other students. If he survived that, then he would have earned himself a place in Azkaban for certain. Snape literally had nothing else to live for. And he had a perfect death in the end anyway, true to his loyalties right to the very end.
Peter Pettigrew, though he apparently defected from Voldemort in the end, deserved to die. Everything he did, such as selling the potters out to the dark lord, sending Black away to azkaban for all those years, even resurrecting him all by his lonesome, all of this played a substantial role in the rise of Voldemort and the events that followed. He was essentially the puppet master throughout all of this, while being described as a lowly servant to the Dark lord. His hand apparently turned on him and choked him to death - a death rather fitting of someone so loathsome. He betrayed his friends, he turned to the shadows, he murdered innocent people, this man deserved death more than any other on this list.
Voldemort, of course he had to die! He was the whole reason this series started. His neo-nazi views weren't going to suddenly change at the last minute. That's the only way he could have possibly survived the events of this book. The whole reason for his death is the whole premise of this book. His death was the making of this book, the very climax of this series, he was the very reason we had Harry Potter.
Bellatrix was a high supporter of Voldemort right to the very end, if she wasn't killed by Molly, then she would have been killed by the hundreds of other people lining up to kill her. I'm pretty sure everyone was finished with her shit after she killed Sirius Black. Frankly I wouldn't be surprised if half the people out there were on a manhunt for her. She deserved her death, she was loyal to Voldemort right to the very end, even when it was apparently clear that they had lost, laughing while she did it.
Nagini was one of the Horcruxes, again, the only way she could have survived is if Voldemort changed his ways, or if she somehow got control of the Resurrection stone, which I don't think either was even remotely possible. She had to die in the end.
Crabbe was a thorough jackass throughout the series, even to the point where he was egging on a clearly uncomfortable Draco to kill Harry and his friends. Though he was influenced by his other friends, his father, and his house, and the blame wasn't placed too much on him, his death still proved that the inexperienced allies of Voldemort would die just like anyone else. He deserved his death.
Lavender had added one major part to the overall plot, and that was being Ron's girlfriend in the Halfblood Prince. Frankly she didn't really pose much of a major character as to someone who should have survived. She was inexperienced, much like the rest of the army, and if she didn't die, then anyone else would have, too. She really was a random death at the very most. Admittedly random deaths aren't exactly the best way to handle things in the Harry Potter universe, but it was either her or another notable student, so it didn't exactly matter too much.
Colin Creevey has much of the same attributes as Lavender, but he had the added issue of being an annoying little prick. I think he was purely one fanboy of Harry's, and got petrified as part of the plotpoint of the Chamber of Secrets. Any other character could have been petrified, Rowling just decided to bring in Colin. He didn't play much of a role in future installments, having his role so substantially reduced that his character and his character's brother in the films were simply replaced with Nigel, whom was actually pretty damn cool. I say good riddance to Colin, really. His situation is similar to dobby's, but with the expense that his role was replaceable.
Gellert Grindlewald was really just the bit character to explain a fair bit of Dumbledore's background and the Elder wand. His death didn't really affect the character's journey, so I say fuck it, why not.
Gregorovitch was similar to Grindlewald, in the essence that he didn't play much of a large role. It also seems like he was supposed to be some sort of replacement for Ollivander? Not sure what role he really played, but it can't have been that big in the end anyway.
Charity Burbage was introduced in the exact scene that she died in in the movies, so she can't have made too much of an impact in the books either. She's no Mcgonagall or Snape, she was really just invented to show Voldemort's prejudice against muggles (as she was the teacher of muggle studies), she was disposable.
I'm not too familiar with the books, as I said before, but like Charity Burbage, Bathilda Bagshot mustn't have had a very large role in the events if her scene in the movies was so damn small. She was an old bird either way, so if her body wasn't already inhabited by Nagini, I'm fairly certain she would have died a couple of minutes later anyways. Disposable. I guess the same could have been said for Scrimgeour, but the fact with him was that his role was taken over by someone exactly like him. I see no need for it, just kick pious out or at least make him a much more minor character.
