Implement Article Preview
Create a Preview link in the Article's tabs, next to Display. Preview should show what the entire, assembled article will look like in outgoing mail in both rich text and plain text.
Default RT only inserts plain text into replies and comments. So it will use the same content regardless of whether the user is editing the reply in rich text or plain text. With this extension, RT will send both a rich text version of the article and a plain text version when the user edits in rich text mode. But there's no way for the user to see what the article's plain text version looks like without a Preview function.