I made two attempts in making a backup of the world. The results were more or less the same.

Good news:
Every block in the chunks I visited appear to have been saved, so at least it should be able to serve as guide for the things we've built.
Animals seem to have been saved in my first attempt.

Bad news:
Inventories of chests and machines seem to be saved in an irregular manner: some have items, but most don't.
Player inventories aside from mine weren't saved.