Its game over. On game over, you can start a new game, keeping all of your goblins minus any that died during the defensive battle if losing one is what caused the game over.
Goblin Burrow: I'll Borne v220720 Uncompressed Event Images + Extra
For those looking for uncompressed event images. I've sourced these files from latest Japanese Completed Edition (v220720). I have compare it to current latest Fan Translate 1.5d, So you can download the zip file and extract image_0.7z files directly to data/image_0 folder.
Still it might be good idea to make a back up first in case I mess up somehow. Also there are uncompressed voice_0 files available that I didn't upload. Not sure if there any interest in these. So just reply to this post in case you need one. Update: Uncompressed voice_0 has been upload