I think the best way to correct the situation was to make a roll.
Illithids, have a buffer. They will stay in battle untill 0 HP's and then if they are wining they stay more. If not they can escape.
Even berserkers cannot do this. If they evade death by raging and then kill the oponent they get some rolls to save them from death. But they can die.
Illithids cannot.
They should have to make a roll.
If they fail, they die. Make its a concentration error while diverting the energy.
A good roll would be 1 chance to die in 20.
That way people would think twice about hiting the 0 HP's spot.
You know, I actually think the berserker rage hp boost is analogous, but not in the way you say. By my understanding, if a zerk snaps out of rage with a certain percentage of hp left, they survive. If not, they are mortally wounded and die slowly. This may be wrong, but it's how it's seemed to me with all my experience playing as and fighting against zerks. I have always found zerk rage to be a reliable boost of hp, that unless I end it with very, very little hp left, I live through. Whether rage automatically kicks in or not is based on rolls, but as rage is also an inputtable command, this does not bother me. Perhaps a better example of random hp-saving stuff would be ogre bloodhaze, which is far more chance-based. Ogres can't rely on bloodhaze, it's just sweet when it happens.
Regardless, I'm against making shock chance-based. It's something that a race that doesn't have massive hp, dex, or the ability to wield weapons needs. I've played an illithid necro at 50, and damn, they are NOT easy to play. When they hit their power peak, they're insane, but below it they are far from easy to play. I like to consider myself fairly good at PK, but I had a lot of trouble with this combo, especially when it comes to coming back from a death/full loot. Getting new zombies, new eq, it's incredibly difficult with an illithid necro if you're doing it alone. Shock has not only saved me from PKs, but it saved me a ton of times from mobs like Drstam that I was just trying to kill to get a basic zombie so I could get back on my feet. Not only that, but an illithid necro attracts a LOT of PK attempts, from goods, Watchers, and the regular gamut of evils/neuts looking for a pk. I've honestly never had as difficult a time getting eq and getting back up to where I was prior to a death as I have had with my illithid necro. NEVER. I've had a large variety of level 50s, melee, caster, communer, and rogue, and NONE were as annoying to eq and get stronger again after a death and loot as that necro was. That alone makes shock balanced to me, because without it, I'd have died a dozen times more.