As long as you're sure that you're testing the correct pins, then it certainly sounds as if the device has been destroyed. What type of equipment is the device being used in? The 78L05 is only designed to output 100mA max. Is it getting hot or does it remain cold?
With regard to repeat failures, the best thing to do is ensure that your 5V rail is not shorted to ground. Be aware that if it is, it might be the regulator itself that is providing the path - remove it and test the 5V rail again. Of course, depending on the application (is it your personal project), you might be overdriving the device. It can provide a max of 100mA so if you're asking for more, it's going to melt.
Brian