This morning I loaded up my world "The Elf Bog" and instead the shared world "Cheesy Goodness" loaded in, instead. I exited, and tried again, and it worked fine. After playing in Elf Bog for a time, I died, and decided to get rid of that world. I backed out, and carefully deleted all worlds except "Cheesy Goodness". They all had very distinct names, as you might be able to tell. I am 100% certain, the only world remaining was Cheesy Goodness. When I logged in again later in the day, only one world remained; "the Elf Bog"; The primary target for deletion. Now I've lost the world myself and my partner were doing so well in. We were on track to survive our first winter ever as a team.