Workaround for fixing the boot for installed HBSD systems with ZFS rootfs:
1. Boot with build-950 (or earlier) ISO and drop to shell
2. Mount ZFS root
3. Copy /boot/loader from to <rootfs>/boot/
4. Remove ISO/CD and reboot
Notes:
- I used the bootonly.iso, but probably others will work too.
- Be careful not to copy loader.conf as ISO contains version without zfs_load=YES, preventing booting into ZFS rootfs.
- Also systems with UEFI might need to copy 'loader.efi' instead of/in addition to ''loader' (I did not test this)
See attached image for commands I used: