> the dying may not produce ashes at all. Unless he's to be strapped to the bottom of the rocket engines...
You assumed they're using oxidation based rocket propellant. Elbonian may very well be using pneumatic (soda mentos) or hydraulic (water rocket.) Neither one of which is likely to reach sufficient speed to generate sufficient heat from air friction that could cremate the passenger.
So... how high can an Elbonian rocket actually get? They're communists right... and they have rockets capable of reaching out of space? Clearly we need to go to war against them now to prevent them gaining nuclear weapons!