This may vary by jurisdiction (I see you are posting from Texas), but generally the medical examiner only conducts an autopsy where the circumstances surrounding the death are suspicious (as in there could have been foul play). You have not provided enough facts to clarify what happened. I would encourage you to contact an experienced wrongful death attorney in your jurisdiction to discuss and evaluate this matter with you in detail.
Posts on this forum are intended for educational and information purposes only and do not create an attorney client relationship. The answers posted should not be treated as legal advice. The posts are intended to be accurate but are based on incomplete information and may be truncated for expediency or to avoid disclosing confidential advice on a public forum. They are not a substitute for speaking directly with an attorney in your area. Mr. Thayer is licensed in Washington state only and laws in your jurisdiction may vary.
Sorry for your loss. Your posting indicates that your loved one collapsed at work, but does not make it clear if he passed away at work, on the way to the hospital, at a hospital, etc. Your first point of investigation is to obtain the ambulance report and if he made it to the hospital, the medical records, to see what is contained therein. Right now, there is nothing to indicate a medical malpractice exists.
In Texas, depending upon the circumstances, many death certificates are signed by the Justice of the Peace, and that person doesn't need to be a doctor or a lawyer. Some JP's will actually conduct an investigation, interview the doctors that were treating the person at the time of their death, or even read medical records, and then they will fill in the cause of death section by what they were told by the medical providers.
When someone just collapses and dies at work so there are witnesses that saw him collapse, it could be from a heart attack, or a stroke, or an aneurysm (bursting blood vessel) and unless there was a very obvious medical history that makes one of those circumstances more likely than the other, you may never really know which of the three it might have been.
If the Justice of the Peace doesn't have any reason to suspect foul play, and if the family doesn't insist that an autopsy be performed, then they are very likely to just put heart attack as the cause of death as a matter of practice.
If a lawsuit arises later, the J.P.'s opinion on the cause of death, especially if the J.P. isn't a medical doctor will be given little if any weight at all.
I'm sorry for your loss. Good luck to you and your family.