@jamieptaylor It sounds like the save just glitched out on its own. Maybe you were over the RAM limit when you saved—TS3 is a 32-bit application and can only use ~3.7 GB of memory before bad things start happening—or maybe there was something else corrupt about the town. There are so many things that can go wrong with this game, sometimes it's impossible to pinpoint the cause. And errors build up as a save progresses, so the glitches usually strike only after we've become very invested in our sims.
The first thing to do is to delete the five cache files in your TS3 game folder in Documents. This probably won't help on its own, but it's worth a shot and won't cause any harm. In fact, while you're troubleshooting, you should delete them every time you quit the game. For reference, those files are:
- CASPartCache.package
- compositorCache.package
- scriptCache.package
- simCompositorCache.package
- socialCache.package
If that alone doesn't help, and it likely won't, move your entire game folder out of Documents and onto your desktop. Launch the game to the Main Menu, change all your game options to their preferred settings (they'll have reset), and quit. (Delete the cache files.) Then open your existing game folder, right-click on the Saves folder inside, and select Copy; right-click inside the new game folder and select Paste.
If your existing save takes place in a store or custom world, i.e. not one that's automatically installed with the game or one of its packs, be sure to install that world as well. But don't add anything else to this folder. Just load your save, which will now be available at the Main Menu, and see whether the sims have reappeared. Don't worry if you get a message about missing objects; this is just for testing, and you don't need to save your progress. If the game looks fine, you can transfer or reinstall the rest of your content in your new game folder and continue playing.
If your save is still missing all its sims even in a clean game folder, the save itself is corrupt, likely beyond repair. There are a few other things you can try though. The first is to load a backup save. Even if you don't have one, TS3 keeps the files from the second to last time you saved. Inside Saves (in your new game folder as well as your old one, since you copied the entire thing), you'll find a folder labeled with your save's name plus a .backup extension. So if your save is SunsetValley, its folder will be SunsetValley.sims3, and the backup will be SunsetValley.sims3.backup. Rename the backup and delete the extension (i.e. SunsetValley1.sims3), and it will be available to load from the Main Menu.
If this doesn't work either, there's one more trick that's a bit more complicated; let me know if you need it, and I'll write it out.
And if you do get your save, the normal copy or the backup, to load in working order, the first thing you should do is use "save as" to rename the save. That way, the game will create a new save file under the new name instead of overwriting the existing file, so you'll have a backup in case of (another) emergency. It's a good idea to use "save as" often, so you always have backups to use. I do so at least once a sim-day, keeping the last 4-6 files and deleting the older ones when I'm sure I don't need them anymore.
The other thing you should do is save your sim to the bin. If you want to preserve her house, evict her and save it separately. (You can quit without saving after you do this.) You may find that this save is only temporarily functional and soon glitches out again. In that case, the best way to move your sim is to place her, and her house if you want it, in a brand new save. The in-game moving mechanism (through the phone) tends to transfer data, including corruption, from the old world to the new one. Be sure to quit to desktop and clear your caches before loading the new save; switching at the Main Menu can transfer corruption as well.
