For years, it was presumed that you just... lost it. You'd never be able to get it back - unless you used a hacked shrub, some game-breaking deletion of characters, other crap that was just not efficient. But, I've known this method for a number of years. I credit it to Mootilda who posted it years ago before her passing, I don't remember quite where, but someone managed to link me to it about eight years ago.
These directions were written for Windows Vista or Windows 7 but have been confirmed to work on Windows 8.1 and Windows 10. You don't even need to close the game to do this, just close and reopen your lot bin and they should be there after a tiny loading time.
This will not include the families living in the lot, but it will most likely include their uni-camera and BV-camera photographs as well as any paintings. Beds will remain in the state they were during play, swingsets, anything at all. The time of day and weather/season will also "stick" to the lot.
Go to Documents/EA GAMES/The Sims 2/Neighborhoods or wherever your folder may be installed
Locate your 'hood - if you don't know which one it is, it's likely N004 or a higher number. Click through to find the Snapshots folder on each if you're not sure.
Navigate to your Lots folder.
Sort by "Date Modified" - if that does not appear, right click a blank part of the folder, "Sort by" and click more. Check Date Modified and then hit OK, and sort by it.
If it's the most recent lot, CTRL+C to copy only that file.
If you're not sure, CTRL+C all of them. *shrugs*
Then, you want to go to Documents/EA GAMES/The Sims 2/LotCatalog and dump all the files into there.
You will see files like cx_0000080.package - sort by "Name" and then make sure you find the LAST one in that sequence.
With your N004_Lot489.package or whatever it's called - take that and change that to match. So, if you have cx_0000080, rename that file to cx_0000081 and so on and so forth until you're all done.
Don't rename character files if there's any in there, though.
And then, you're done! Open up your Lot bin ingame, and they should all be there.
I hoped this help somebody.