I had something like this happen to me. I have the disc version of the game, but Origin wanted to update it to the latest version which then proceeded to uninstall Into the Future and replace it with the digital version. I stopped it before it could remove anything else, but I had to completely uninstall The Sims 3. I then turned off automatic updating in Origin and re-install from the disc. Unfortunately, turning off automatic game updates in Origin is an all or nothing affair - you can't turn off automatic updates for an individual game.
Hope this helps and happy Simming.
Flynn