Please add an undo save/rollback to the message editor. (I'm using the HTML editor.)
For reference, here's a screenshot of Shopify's file editor with the "Older Versions" link clicked and the dropdown opened. It offers every save going back as far as I cared to look.
This would be extremely useful in those cases when I have two messages open and I'm referring to one while pasting (from my text editor) into the other. Once or twice I've saved a change in the wrong message and had an "oh, ****!" moment.