Robinson Crusoe

Are losses retroactive? If I lose something, do I reverse its benefits?

For Items that are flipped back to Inventions: yes, lose/reverse as many benefits as you can, but don't worry if there are some you can't. (This isn't unfulfilled demand.) For terrain types that become unexplored, there is no retroactive effect -- you can still keep the Items you built based on those terrain types, but you won't be able to build more.
Related Rule(s)