If the fan is small or broken, it can cause your laptop to overheat and shut down, or possibly even die. Keep it elevated on a cooling pad, repair the current fan if it is broken or install an additional fan. You could also even take a standard fan you currently have and direct it to the hot spots, if you will.

As for longevity, it depends entirely on how the laptop is used, with a little bit of good/bad luck as well. 3-4 years is a general rule of thumb I use in terms of the technology being out of date, but if you take great care of your laptop it can remain functional for 8 years.