They are. Edits in comic books could range from color adjustments to reworking dialogues or adding/removing panels to better suit the overall theme and flow.
Shigaraki is not dead in the manga. The storyline has many twists and turns, and his character plays a significant role, so his survival adds to the ongoing drama and suspense.
Well, for copy editing a novel, you need to focus on language accuracy. That means correcting punctuation, fixing word usage, and ensuring the sentences are structured properly. Another important aspect is to maintain the author's voice while improving the clarity and flow of the text.