@ aaro54: I've found it best not to replace anybody permanently, actually. Usually, I swap her and Lance out, though. Matt works well as a meat shield, and most of Natalie's abilities are highly useful in most situations.
I have to say...Out of the games I've played recently, this one is probably one of my more favored. The characters, to say the least, were very well written. And the story was enthralling as well.
So, I have to thank you for developing this game.