We are pretty close to saying bye to beta version of JA Builder and release an RC version next week, which comes with some major changes and features.
One of the features is "revisions", which are stored for restoration at any later time. This feature can be tested on the JA Builder demo and would be part of the release next week.
The new feature will auto save the changes you did when editing the page (for now, each revision includes 10 changes). Meaning, after you do 10 changes, it will be saved as a revision. You can revert to previous revision to revert the content, pretty handy feature.