Who has the final say in the decision to kill a character?
Depends on the character. But ultimately, the EIC has more say than the writer or the editor. If you’re talking about killing off a minor character, like a rank-and-file villain or a supporting cast member of no real importance outside of that one title, the writer and the editor will make that decision among themselves. But if you’re talking about a more significant death, then you’ll want the EIC to know about it and sign off on it beforehand. And for really big deaths (Captain America, etc.) you’ll likely want to let people in other divisions know about it ahead of time.