If its electrically " dead" then it may not be possible to remove the key or even lock the car. You may have to remain with the car till its recovered? Have you tried phoning the emergency MB number they may be able to advise.
According to this diagram the ignition lock is powered by fuses 19= 20A and 27=7.5A they are both in the underbonnet fuse box?? W204 C300 Fuse Diagram/Layout - MBWorld.org Forums
Caution - they may have blown because of a short caused by the accident- proceed with care!