The limo didn't slowly decelerate for 60+ mph…it hit that embankment and STOPPED…abruptly, from a high speed to zero!
No seat-belts on (or required) in limo passenger area…everyone involuntarily rockets into the driver partition, all at once, even if they are holding on to something, and STOPPED…The internal G-FORCE injuries, alone, that each would have suffered would easily be enough to turn their brains and other organs into mashed potatoes, even without crash impact injuries.
Instant death…no possibility to resuscitate.