Depends how much RAM you have, how hot your laptop gets on the inside, and where it's being used.
For example: If you have very little RAM, the hard drive is going to be churning constantly. If, on top of that, your laptop generates a lot of heat and is used on a soft surface in a hot room, the heat will make things worse for the hard drive and it will fail.
On the other hand, if you have a very well cooled and energy efficient laptop with lots of RAM, it'll be fine for a good long time.