Yes, the best results are gained by embalming remains as soon after death as possible, However, an autopsy changes this ans we do not know the extent of the exam. Normally all internal organs are removed, including the brain. There are times when only patial exams are done, or only chemical exams. However, I would be very surprised if the medical examinar didn't do everything they could do because of the high profiile of the case. If the cause of death was chemical abuse of any kind, there may have been chemical burns on the skin of the face, etc. This would make viewing difficult, but not impossible.
From my 20+ years of embalming, once an autopsy is done, the embalming results are never as good and a delay of a few hours after removal from a medical examinar (flying time from California to the east coast) would have little impact on the results because the blood has been drained and blood clots are very no longer an issue. Messy, yes, but a good body bag would contain the situation just fine during transport. Decomposition of remains will start almost immdeiately after death but not enough to cause issues for an experienced embalmer even after several hours. If the remains are refridgerated, days can go by and the remains can be embalmed and viewed.
I doubt that any embalming took place in the medical examiners office...OSHA would be all over that one!