Good morning, @CharlieHedman ...
This isn't necessarily an answer to your question/comments, but I understand the frustration that you have described. I'm not sure if you are aware, but when you are typing text into the Rich Content Editor (RCE) as part of an assignment that you are submitting to your instructor, Canvas should auto-save that text if you navigate away from the page. I just tried this in my own sandbox course, and it worked as expected. However, this isn't a guarantee that it will auto-save in all situations as described under the heading "View Auto-Saved Content" in the following Guide:
How do I add and modify text in the Rich Content E... - Instructure Community (canvaslms.com)
I agree that first writing your response in an external software like Microsoft Word might not be the most ideal, but it is a workable option at this time. I might also suggest just the reverse of this... if you were writing your response directly in Canvas first, before you press the button to submit the assignment, copy and paste your text back into a Microsoft Word document and save it to your computer...so that you have a back-up should something like this happen again.
I don't know your instructor, and I don't know the context of your course. So, I don't know the reasonings why your instructor requires that you use the RCE to submit your assignment. Depending on what the assignment is, I might make a suggestion to the instructor to use a file submission instead. This way, you can write your text in a Microsoft Word document and then submit the entire file online. There wouldn't be a need to paste in the text to the RCE in this scenario. Your instructor would have additional tools available to him/her to grade your assignment that normally aren't available with a standard text submission assignment.
Anyway...I wanted to give you this information...for what it's worth. I hope it will help in some way.