God decides when people die, but it is not his fault that there is death in the world it is ours, there is sin in the world and the punishment for sin is death, we die because we sin it is as simple as that. If someone is murdered then that is because someone has sinned by killing them.
Overall the reason we die is because we sin.
It is the same for sickness that is because of sin that there is sickness as well, i am not saying he is directly punishing that person if they get sick, i mean that it is sin in the world as a whole that causes it.