There are also some Tips for Students Writing Discussion Posts that can help minimize the frustration in the if you were typing the post directly into Canvas (as opposed to a Word document), it's almost certainly gone. A related feature request is ' modifiedtitle='true' ti., which is not in the top 10% of feature ideas and may get archived. There is a feature idea for autosave , where Canvas has said, in undated and confusing language, that it's not happening anytime soon.
The one recommended in November 2017 in this thread is no longer on the Chrome store, but you could do a search for form recovery and possibly find something. There are some add-ins for browsers that autosave form content for you, but those need to be installed and running before you've lost the content, so they wouldn't help in this case. Canvas doesn't have autosave capability in the Rich Content Editor, which is used for discussion posts or essay questions on quizzes. If you were typing the post directly into Canvas (as opposed to a Word document), it's almost certainly gone.