Death in the vast majority of cases entails general ischemia due to the cessation of circulation, trauma or no. How sensitive your brain is to a lack of oxygen is easily tested by having someone compress both your carotid arteries for 60 seconds. (The exception to the death-ischemia link would be brain death with circulation upheld for a variety of reasons, most commonly viability for organ transplantation.)

The killer consideration with fatal traumatic injuries is their unpredictability. Such an event will most probably drastically prolong the time to cryopreservation, at least by hours. Where are you? Which hospital are you announced dead in? Where's the nearest cryopreservation team? When in the process are they notified? How long is their travel time? How much damage is done while you're not yet announced dead?

The delay, hours of ischemia (while being dead), is what will degrade your brain tissue to a microscopically garbled mess, regardless of the specific type of trauma.

It bears repeating: Even the penumbra of neurons = the peripheral neurons that after a stroke still get some measure of oxygen are given up upon after 4-5 hours (no benefit from further treatment). The central neurons most affected by an ischemic event are considered lost within an hour.