I’m going to give you two answers; one in the context of the story and one in the context of a filmmaker.

1: The specifics of Moss’ death are irrelevant, just as the drug deal, just as the death of his wife. They’re certainly changes in the narrative that need to be addressed, but the details of what happened are extremely clear. The violence we see on screen is always to frame Anton as a ice cold killer and to fear him; that’s important. You know exactly what happens to Moss; why do you have to see it?

2: You’ve just spent a few years exhaustively trying to fundraise and schedule a motion picture and, based on the narrative and characters therein, a very minor incident to the plot happens which would take tons of stunt coordination and planning and setting up shots and changing mags and extras and . . . The Coens could’ve given you the linear, beat-by-beat rundown of Moss dying and Chigur retrieving the case, but they instead do it with more focus on how Bell sees it. Bell’s the lead, after all.

There’s nothing missing from that film. It’s nearly perfect.