They would lose any magical powers they may have had in the book, and you can take them out at any time in the story’s plot, but for all other people consuming the media, it will be shown that the character suddenly disappears, with the rest of the plot being affected accordingly. People will notice this happening. The character is not under any sort of control by you once you have taken them out of the story, although they will appear next to you to start with.
I was going to say Jar Jar Binks, but now I won’t.
I mean…you can kill him once you take him out of the story.
“Yousa wants me dead-dead? Oh pooie!”
proceeds to trip over your furniture and inadvertently set your house on fire