I have 4 pieces from Craig, Brogar, excavation site, and Dorgan. That leaves Luis who still has one. According to a walkthrough, he gives it to you after the dialog option to give him 2 bottles of beer. However, I made the mistake of offering just 1 beer. Now the 2 beer option doesn't show up any more. How do I get the last piece short of killing him? Is he an important character for later in the game?