Ok, I put together a workaround for folks who still want to use this and other older script-fu creations:

1. Download a portable build of Gimp 2.8. You can find one here: https://www.partha.com/

2. Load this and any other script-fu stuff you want into the scripts folder of the portable gimp.

3. Open the floor plan black and white image with portable GIMP and run the dungeon script.

I'm playing with this for the first time in a few years again, and it looks as awesome as ever.