Six hours down the drain... Any way to prevent this in the future besides the obvious?

Jalida,

Its probably a really good idea if you save more often and remember to back stuff up in multiple places from now on. Might also be a good idea to save each of your lots to the library before you save the map as well, assuming you're working in Edit In Game. I've run into a lot of problems trying to get it to save in EIG, while working with create a world.