I don't know if it was a rogue update or something but I had the same (or
similar) problem. Booting dropped me to the grub rescue prompt and my
i386-pc folder was also empty.
Only strange part of my setup is the main drive is GPT partitioned with
regular BIOS so I have a small bios_grub partition at the beginning of the
drive for the stage 2 bootloader.
Somehow my /boot filesystem got corrupted and after a fsck and copying the
files from /usr/lib/grub2/i386-pc to /boot/grub2/i386-pc I was able to boot
again.
Thanks,
Richard