I was in the middle of an upgrade when I accidentaly pressed ctrl+c. I can no longer open a terminal and I cannot shut down with a GUI

As the title says I borked an upgrade. It paused for a moment to ask me something about gnome settings, and I pressed "D" for details, and then ctrl+c to try and get out of the output it gave.

Now I cannot open a terminal, nor can I shutdown through the GUI. Firefox is working fin though obviously. Alt+F2 also works, or at least the command window pops up

*What Should I do to keep my system working, and to start up the upgrade again?

**In my haste I forgot that I have a recent back to restore to and do the upgrade again after restore. I will try that route and update here for posterity.

Final Update

Thanks for the help everyone. I've decided to call in the firing squad.

I formatted the drive with my laptop, and then attempted a fresh install of 18.04 so that I could recover my settings and documents with the Deja Dup backup I made before starting the upgrade.

This introduced another error where I'm stuck in TTY after boot. There will be yet another post about that. Please follow me on this cortisol-fueled adventure of the failed upgrade.

Cheers.