I was able to destroy the Cirlce's base on Lake of the Moon on Hard, reducing it to nothing but... spawning Caravels. Obvously, or I would've won, The Fountain is still there. I rescued it and the possibly immortal bass form the Circle :).Explore this savegame and find that the Circle is completely gone.... even with ES's defensive triggers. Gone in 1:11:57
I know when you load it it says sandbox in the corner. All savegames do that regardless of the Difficulty.