Anyone have any ideas how to handle this? Given how lethal the system is, I feel reticent to leave this entirely up to my own fiat. A NPC panic at an inopportune time could easily spell death for a character. Similarly, an NPC keeping it together could totally save a character. This is probably less concerning in cinematic play where players expect to end playing a different PC than started. But, would be more concerning in a campaign play where the players are more attached to their characters.
Here is something I am thinking of.
Each NPC is assigned a Will score, representing their Willpower. Most are 2, with weak-willed being 1, and strong-willed being 3, with maybe truly exceptional (Ripley) being 4. When an NPC takes an action, if they roll 1s = or > Will, they make a Panic roll. Their Panic roll is 6-current Will +d6 + 1 extra d6 for each 1 rolled above their Will. NPCs permanently lose a point of Will when they are broken, or certain traumatic story circumstances occur (a buddy dies, something catastrophic happens, etc.)
For example, Reid is Will 2. She shoots her shotgun at an alien and rolls a 6, but 3 x 1s. This triggers a Panic roll. Her current Will is 2, so 6-2 = 4. So she rolls 1d6+4 +1d6 because she rolled 3 x 1s, one more 1 than her will of 3. She rolls a 4 and a 2, with +4 = 10, so gets the FREEZE Panic effect. If she had only rolled 2x1s, and her first d6 rolled a 4, that would be 4 + 4, totally 8, for a TREMBLE Panic effect.
EDIT: added example