When you find Han in the Mos Eisley Cantina, switch to use him as your main character once you are outside of the cantina. Let Han die and when it starts you off again with Luke, go back into the cantina to get Han again (he should be there). Switch to him again once you are out of the cantina and his life meter will look empty, but he's invincible. The only thing that I remember killing him is prolonged amount of time on spikes, and of course falling in holes.