We've added change history to your template settings: header, footer, CSS, custom template, even your newsletter description.
This is a live demo. You can view this page on our live demo site, too.
Open the History button on any of those pages to see every revision and when it happened. You can search through past edits, preview older CSS against a real email (or the raw code), and restore a previous version with one click if something goes wrong.
As always, feedback welcome.