So it just shuts down out of the blue?
Please give us some numbers: how much free space is there on your disk?
WHat are the hardware specifications?
When was the last time you rebooted the computer?
Now for the file:
You have to remember to save your file. As you have noticed, Illustrator does not do that for you. Save often, save early, save multiple versions (because if the file gets corrupt, then having saved every 5 minutes still is futile).