You might want to cross post this in the programming section.

oh you want a the walking dead game, but only for pyschology studies.
nice idea ! actually i think about to make a project, that could be similar to the walking dead game, but not with the source engine, i think the cryengine 3 is the ideal candidate when it come to immerge the player into a realistic environment.
Maybe you can explain me some differents types of situations, you want to create into the source engine.
It might help me to know if you need some big features or if it's just some basic things that could already been handled with the actual tools and game logic entities of the source engine.
a vgui dialog for the player to answer to an actor, the sentence that fit more with his own perceptions senses and with a important factor, the Story.

I am not sure at all if the player is not invested into a story, that his reaction will be appropriate. A game is a game, and so much games fails on that important logic point.
a fps is not a role playing game, the actions are limited, you shooting, because this is the only method to continue in the story some people care about the story, other hope for a good type and novative gameplay.

//red