Well, that's a shame. It's a lesson learned that whether we like this we're on a test world that anything is bound to break. Even so, I like to consider this a main test world before we actually play on the real Rising World with that one world ocean with all those islands & island continents. Until then, we're at the mercy of dungeons not handling properly and etc, and that patience should be key. One should expect things to break with ease, yet I do love where Rising World is going.
Good luck fixing the dungeon. I got irritated my dungeon was 'voided' that I simply grabbed dynamite to blow up a section I could work with. Just waking up the nearby sandstone to open up a bubble large enough to allow the re-restored chest area to be active again. Well, at least i have a functioning pyramid again. That's something.
I'll be more cautious with dungeons while building around them, not on them. Nor to use them as base of operations.