Ubuntu 16.04.3 Kernel panic during boot (after trying to auto decrypt disk on startup)

Question

Followup to an earlier question on having my encrypted disk auto-decrypt on startup. It seems I completely shut myself out of my system, I'm getting a kernel panic on startup.

Here's what I did:

First I added a trivial password abc123 to unlock my partition using

cryptsetup luksAddKey /dev/sda3

Then I followed exactly these steps ("How I did it on Ubuntu 16.04.3"). Note that I inserted sudo where appropriate.

That is:

1. appended ,keyscript=/root/lukspw at the end of the line in etc/crypttab that contains sda3_crypt (.....) none luks (sda3 is the disk for which I was prompted during startup to enter the decryption password)

2. Created the file /root/lukspw with the content:

   #!/bin/sh
   printf "abc123"
   

   and made it executable: sudo chmod +x /root/lukspw

3. And finally:

   sudo update-initramfs -u -k`uname -r`
   

I did not get any errors during any step of the process.

Now upon reboot, either in normal or 'recovery' mode (through the Advanced option at startup) I get this:

And I can't do anything, no interaction, no response on keyboard activity.

Have I done something terrible? Is there still a way out of this?