A friend of mine had the same problem today. He also did not have a working backup.
What we did in short:
rebooted phone from hybris recovery image.
(we needed an older one than 4.6. Only 4.3 was available but that worked just fine.)
Start phone to recocery mode
Connect USB
Choose Option 3: Terminal/Shell
telnet from computer to phone
mount crypted device to chroot
sftp all relevant data from /home/defaultuser to computer
reflashed device
sftp data via shell back to /home/defaultuser
@nephros pointed to the relevant documentation and suggested also a solution via SD card.
The sftp thing was easier for us and we didn’t succeed in mounting a SD card.