Vindicated! One a side note I think the issue is located in the post image runonce script that sets up the bootloader. We can attempt to reinstall the bootloader from the pendrive via chroot. Try this:
Create the following folders on the pendrive:
  /chroot
  /chroot/dev
  /chroot/proc
  /chroot/sys
  /chroot/pts
Place the following script on the pendrive:
mount /dev/sda1 /mnt/chroot/
mount --bind /dev /mnt/chroot/dev
mount --bind /sys /mnt/chroot/sys
mount --bind /proc /mnt/chroot/proc
mount --bind /dev/pts /mnt/chroot/dev/pts
chroot /mnt/chroot grub-install /dev/sda
chroot /mnt/chroot update-grub
chroot /mnt/chroot update-initramfs -u
dialog --msgbox "    Deploy Complete \n Press ENTER to Reboot" 60 30
reboot