The idea is that the player fills in their response in their imagination. Though, I think it's a little fourth-wall-breaking when NPCs comment on the player's silence. No future-AI needed.
I know, but as I said, the n.p.c.s don't respond to the player's imagined responses so it doesn't solve the problem that he conversations are implausible and silly.
Either the player doesn't imagine a response, and the n.p.c.s are talking to a wall and act as if that be normal. Or the player does formulate a response, and Gordon Freeman is talking to walls, and acts as if that be normal.
