Well, a normal ol crash probably not. But of course something really bad could happen at any time. You could lose your entire HD instantly turning the computer on one day.
If you don't want to lose anything or possibly everything, you absolutely need to make sure that your computer is completely backed up to an external hard drive or something.
You can do whole machine backups or you can just export all your outlook settings and emails from outlook itself to an external drive every day, week or month. But doing it just ONCE will put you in a far better position than not having done it at all