Sounds like a saddle embolus to me... There are three kinds of thromboembolus: massive, major, and minor, based on size. Massive DVTs embolize up to your right heart, through the right atrium and right ventricle, and then become lodged at the bifurcation of the pulmonary arteries (like a saddle), basically blocking off all blood supply to the lung the artery supplies.
This will kill you very quickly. Here is a spiral CT scan of a saddle embolus at T4, you can see it blocking the bifurcation of the pulmonary arteries:
http://circ.ahajournals.org/content/107/25/e224/F2.small.gif
The guy could have also had a cardiac arrhythmia like a ventricular fibrillation, which could have also caused instant death, or a ruptured aortic aneurysm, or cerebrovascular accident. I'd put my money on a saddle embolus, though.
Get up, walk around, stretch, and take some baby aspirin on these long flights!
Sorry to hear that some guy died on a plane. That is not the way to go out. I can't imagine a dead body just sitting in the back of a plane either... what else could they really have done though. Crazy story...