Probably depends a lot on what options you had enabled on BTRFS. Metadata (i.e. what files are stored where) is normally replicated so you may be able to rebuild the information.
Step 1 is always to copy the filesystem somewhere else, and then work on the copy. That way, if you screw up, you can always make a new copy and start over. Don't write anything to the drive you're trying to fix. Always work on the copy. In fact, once you've made the copy, disconnect the original.
You could image the whole drive/partition, then restore from your backup and try to recover some new files not yet in the backup from the image using photorec or so.
Not enough info, but I'm guessing no. Looks like you started zeroing out the drive and cancelled realizing your mistake? If you had just deleted the partition, you could fix that with ease, but zeroing is pretty much a guaranteed no.
You can try and run some data recovery tools to find some specific files, but I'm pretty sure it's just wasted time.
If this is a HDD you could recover it.
If SSD - no.
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Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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