That depends. Yes, it may be possible to determine if the drug caused death. But what if, for example, a person in the test group has a massive coronary and dies, but no one in the control group dies? Was the death caused by the drug? Probably not, but can you be sure? It's possible that there is some unknown reaction which the drug has with persons of a certain genetic type, say, which weakens vessels in the heart. There may be no way to determine this in these studies, but there's no way to say that the drug did not cause it, either. It's safer to show that death might be a side effect.