What warrants a mandatory autopsy?

Most state laws require an autopsy if a person dies of suspicious causes, not in a hospital or when it is not apparent why the person died. However, you can avoid an autopsy on religious grounds. Some Jewish religions forbid damaging the body and can usually prevent the Medical Examiner from performing an autopsy or at least a fully autopsy such as you described. Unless there was a very strong concern of foul play and a crime, you could probably have a relative speak for you (you will be dead!).