Wow! I suppose it depends on the laws in your state whether an autopsy is required or not. Generally, if the doctor i willing to sign the death certificate with a cause of death, then no autopsy is going to be conducted.
Have you checked with the coroner or medical examiner in your county? If not, then get a hold of them and find out the policies and practices. it might very well be that you would have to front the money for a private autopsy to be done.
I'm guessing you're not in California. Unfortunately, death laws vary a great deal from state to state so without knowing what state you're in we can't begin to look into it.
- Carl