GM/player dispute during a mission, Force 12 lightning ball vs case of 7-7 Options

[ShadowDragon]

On the last mission my players took, the PCs were supposed to plant a suitcase full of 7-7 gas inside a corporate building. The Johnson told them that the suitcase had incriminating evidence that Lonestar would find during an upcoming raid. What the Johnson didn't tell them was that the suitcase was full of 7-7 gas and was designed to release enough gas to kill anyone inside of the building after being triggered by a combat spell. Lonestar was never actually intended to find anything but dead employees. Anyway, the PCs got caught sneaking inside the building and were shot up pretty badly. The group mage had the brilliant idea to pull a kamikaze by throwing a force 12 ball lightning in the middle of the combat, which would catch all the security he could see, as well as the team EXCEPT for one PC. Unfortunately the suitcase was being held by one of the PCs caught in the ball lightning so it released the 7-7 gas, killing the PC outside the ball lightning.

Here's the problem - the player of the PC killed by the 7-7 thinks that ball lightning of that magnitude should have rendered the 7-7 gas inert. I said no, but agreed to post here to see everyone's opinion.