On Adelheid's suggestion, I submitted a "Feedback/Suggestions" in Support:
I love love love that imported works save as drafts. However, I’m frustrated that my edits are all or nothing — if I make edits, my options are “Preview” or “Cancel,” which makes a lot of sense; but then in Preview mode my options are Post/Edit/Cancel — I would LOVE a “Save as Draft” option, so that if I wasn’t done editing I could save it to go back to and not have to make my initial edits all over again. (One person suggested that hitting “Cancel” when in Preview saves it as draft, which is true, but it doesn’t retain any of the edits I’ve made, just reverts back to the original imported version — I tried today and last week.) Thanks so much for thinking about this.I got a reply less than 48 hours later:
Sorry about the trouble you’ve had here! The issue has been looked into and we can confirm that this is a side effect of intended behaviour – if you make a change to a posted story, then decide you don’t want to save, it won’t save. However, this also means that if you make a change to a draft, then don’t post it, it treats that the same way. Being unable to edit a draft is a bad thing, though, so your suggestion have been added to our list of stuff to consider changing.
In the meantime, sadly you won’t be able to edit drafts without either posting them or cancelling and losing your changes.
We’re glad to hear that you like the feature of saving imported works as drafts, though.
AO3 Support volunteer