So I booted the live USB again and:
1. scan and assemble the array
* mdadm --assemble --scan
2. mount /dev/md0 /mnt
3. mount /dev/sda1 /mnt/boot
4. mount -o bind /dev /mnt/dev
5. mount -o bind /sys /mnt/sys
6. mount -o bind /proc /mnt/proc
7. chroot /mnt
8. apt-get purge grub grub-pc grub-common
9. apt-get install grub-pc grub-common
* (install grub to /dev/sda)
10. exit
11. reboot
Not it boots up and runs without issue
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