Your Sims and lots are in your tray folder. Anything you saved online to the gallery should still be retrievable regardless. If you want to protect your custom content and personalized content, rename and move or zip/rar the following folders out of Documents/Electronic Arts/The Sims 4 unless they are already empty :
- Tray folder
- Mods folder
- Custom music (offline radio playlists) folder
Once those are backed up, online or offline to external drive, then try repairing your game. If that does not work, reset your game to factory state.