Actually I was able to recover it. Weird, before I killed emacs I checked the autosaves and my new code wasn't there. Maybe somehow the kill signal triggered emacs to autosave just before quitting?

So C-x C-s before C-x C-e is a good emacs habit

I found pkill -SIGUSR2 emacs usually brings emacs back and lets me save if I do that.

Oh thanks, I'll try the SIGUSR2 next time

Always worth having sane print lengths set in your REPL, can occasionally save you if you print the wrong thing.