I wonder why your runners didn't simply shoot the mage with a DMSO/narcoject or neurostun cocktail instead, then capped him in the head once he was down. Or use deadly poison right away.
To be honest, because the player who did it really enjoyed leaving important NPCs alive as worthless husks. This same character had a Biotech skill explicitly so he could remove an opponent's cyberware after defeating him, without killing him, then implant him with 5.98 Essence worth of used datajacks, then dump the twitching, blind, limbless body in a back alley with the rest of the hobos.
As a GM, he'd do the same thing to players all the time - playing a Mage in one of his games was pretty much a guaranteed ticket to getting kidnapped and stuffed full of 5.98 Essence worth of completely useless cyberware.
