Provide some documentation in the reference doc + in the RN to explain how to put it back if needed. From Marius:

The list of styles is configurable. See https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_config.html#cfg-stylesSet CKEditor 4 API docs . Defaults to xwiki-platform/xwiki-platform-core/xwiki-platform-ckeditor/xwiki-platform-ckeditor-webjar/src/main/webjar/styles.js