Only ur usb graphics burns and dies out . There nothing to mine with it .
Use ASIC for them. If you use a fan and a heatsink attached to it, it would have a longer lifespan. But if you can't afford to buy a expensive cutting edge ASIC, you probably shouldn't mine.
what if he just wants to help out the network yo ? who cares bout the money when you can join a revelution.
Having a GPU or small USB ASIC to mine would be a relatively bad choice. The network hashrate is very high, the impact would be pretty minimal as the GPU/USB ASIC's hashrate is extremely low.