MAJOR RULE OF WOLVES SPOILERS
I know a lot of people have been saying that David's death was unnecessary... to be quite honest I thought it was completely necessary, and quite frankly, not enough.
First, this man was nothing but good. He was a scientist for the sake of science, but never toed the line toward hurting other people after he realized how much he hurt people after he created the stags amplifier for alina. He was incredibly influential and will have a massive impact on Ravka, science, and the people around him. Zoya hated him when she first joined the triumvirate but she was heartbroken and enraged when David died. This is what war does. It kills people that don't deserve it, especially at the times you don't expect it. Having David die AT HIS WEDDING is horrible but it certainly proves this point.
Secondly, I felt that David's death was not enough. Obviously I hate characters dying, but I felt like there were no repercussions to the war with Fjerda. It ended with David dead and Zoya as queen, but EVERYONE made it out of that final battle. It just felt like there was no toll to be paid at the climax. Maybe if David had died during the final battle, I would feel differently, but I don't know. It just felt like the battle had no repercussions, and it could have been solved with a meeting with Fjerda and Zoya showing off her new power.
I know this certainly isn't the criticism most people have in regards to David's death, but it was something I tried to think about critically after I finished row.