No Ctrl-Z should undo what was typed. Overriding it with some auto-save feature will not really do what you want and will be confusing.

Ctrl-Z works. I just tried it. Edit document, wait for "saving" to complete, it says "Saved" and then Ctrl-Z went back before the save. I even tried a Ctrl-A then deleted the lot, waited for the save and then fully restored with Ctrl-Z.

Tony's fix would get complicated. How does it know when to save? A simple delete all is easy to detect. What if it's a whole paragraph? When does it start autosaving again? ...and so on....