Teachers and course developers have the luxury of saving drafts for their assignments, pages, discussion instructions, etc., by clicking the Save button instead of the Save and Publish button. For discussion responses, the only two options are Reply and Cancel. If it's important for students to have a response draft, then it would be good for them to type it out in a document and then copy/paste it to Canvas. Google Docs and Office 365 have the luxury of autosaving to their cloud spaces, so that could be a reliable approach.
