I've now had 2 clients delete users associated with content without realizing that they were deleting the content as well. At the very least the default radio button should be to associate the content with another user. But really, deleting the user with content should be red and blinking and "are you sure"?
I understand that this is a training issue as well, but it's just too easy for someone to delete right now. A re-designed interface could go a long way to avoiding this issue.