I sometimes hit Ctrl+W without thinking, and lose pinned files. In most cases going back through the command history or recent files is enough to find them, but it would be ideal if Creator could (via an opt-in setting) prevent me from closing that file, ideally with the same kind of alert/feedback (e.g. system sound) that is used when e.g. you hit backspace in an empty shell on macOS or click outside a modal dialog on Windows.

This way, the only way to close the file would be via the context menu or file menu, both of which are a lot more explicit.