Any number of things can happen when you fall. If it's any kind of head injury you could have a bleed and die from that, if the fall hit a major organ or artery. I mean, he wasn't exactly in his prime, so injuries of that sort can be much more devastating. I've known/of many 70+ers who died of pneumonia which was usually contracted as a complication of some other thing/sickness.
Eh... Just such a sad piece of news. I didn't know the man personally, but as with all of us i'm sure we all know he had his influence in our lives. For the more artistically inclined he may have even inspired creations of our own. He cut a swath in the artistic world that nobody else can ever touch quite like he did, and he opened our eyes to the many wondrous possibilities that exist between beauty and horror. I'm very sad we never got to see another one of his wonderful unvarnished creations brought to life. Rest in Peace H.R. Giger...