I'm a grunt with no medical training who wants to be an 18D; I hope I'm not stepping on any toes by taking a stab at this.
According to google and my CMDT, the decorticate posturing and unresponsiveness point to contusion or lesions at or just above the brain stem. The unequal, unreactive pupils indicate a rise in intracranial pressure, which is potentially life-threatening.
I'm guessing the blood from his nose and mouth suggests the impact was to the face, which seems consistent with both bicycle and vehicle accidents.
The stabilization options I can come up with are the same for both scenarios, except the IED one starts off with "METT-T depending": roll the patient from his side onto a spineboard; he's now on his back and bleeding into his mouth, so airway management is obviously a concern. How risky is it to emplace an endotracheal tube on a guy with a brain stem injury?
I'll leave the treatment and care questions alone.
Fran
