I have used the Sign Out option before when my game crashed. Of course, if you have other documents open (such as Notepad, Word, or Excel) that you haven't saved, a message will appear asking if you are sure you want to continue.
At that point, click cancel. It will take you back to Windows, and your game will be closed; however, all your unsaved documents will remain open. I think at that point it has already closed your browsers and the file explorer.
Go into The Sims 3 folder and delete your cache files before starting your game. I usually delete the script error messages at the same time.