There is a lot of traction on this request to
Auto Save in Rich Content Editor but an intermediate step between here and there might be a warning when you are leaving a page with any unsaved changes. Here is the issue as described by
Christine :
...it would also be helpful if Canvas warned you before navigating away from unsaved content. Chrome, Safari and Firefox display a confirmation dialog when you try to leave a screen with unsaved content, but only when editing Pages. It's too easy to navigate away from unsaved content when editing the Syllabus Description, Assignments, Quizzes, etc...