In a recent release to Beta, with the intention of release to production, we've added the ability for users to undo an edit within 5 seconds of submitting. The work can be seen in T284532. Based on the interaction, when a user clicks undo it takes them back to the page they were editing and what they wrote becomes lost.
If a user clicks undo, save the text they posted and bring them back to the "Compose" field with the text they wrote in edit mode.
User clicks reply
User writes "Hi User" in Compose Response box
User hits publish
User hits Undo
User is brought back to Compose response box and "Hi User" is in the box