Actually you're being surprisingly coherent...
Ok, that makes sense, sort of...although I think Matius has a point there too...plus, I think it was intentional that it happened so suddenly and out of the blue...there has to be a reason. Which is why I think my theory makes some sense too...up till then, we were made to think he was practically invincible...then he almost gets killed in a random car crash...
I understand the point of the film (it's pretty obvious), but I think they still could have at least shown Llewelyn's murder (if they robbed us of the would be climactic showdown between BARDEM
and Brolin). He was disposed of as a meaningless side character, and I think it wouldn't have hurt the story and point to give us that much...the bad guys would have still won...*shrug*