Mojave macOS Installation Error (com.apple.DiskManagement error 69854) I tried upgrading from High Sierra to Mojave on my MacBook Pro mid-2012 Non Retina, 16GB RAM and 500GB HDD, core i7.
Unfortunately I don't have a backup and I keep getting this error "com.apple.DiskManagement error 69854" during the installation. I can only access into Recovery.

How can I solve this error and install Mojave without losing my data?
Had the same issue. Retina 5k imac. 
Rebooted with cmd-r and restored from time machine. Everything is back and working even boot camp!

Will be waiting before trying Mojave again.