OK. It is not Btrfs then. It is ext4. It is risky, but I think your home directory should be on a different partition/filesystem, so your personal files should be safe. You can try running e2fsck -y /dev/mapper/qubes_do0-root and hope it fixes the filesystem. Reboot when the command finishes and hope that your system will be working again. Good luck!
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YOU ARE GREAT! WORKS! 
Thank you very much for your time and invaluable help! 
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