First off i appreciate your thoughtful response, however i disagree.

You say: "But since we don't see Christopher ratting, and all we've got to go on is incidental symbolism from which to extrapolate meanings to suit our purpose, then he isn't a rat. It's not significant enough to be a storyline in itself though, otherwise Chase would have made it a story line, and it would have been major. Chase isn't that subtle."

Wrong, Chase IS that subtle, especially in the final season. EVERYTHING means something. it is a story line in that it is NOT a story line. Chase loves these background stories -things that are going on that he doesn't show us. he want's us to follow clues to discover what is really happening. he constantly throws red herings to challenge us.

As for someone else coming to clean up the mess, i suppose that is possible. but why not show that phone call or the meeting? didn't that JT murder story line seem to be left hanging to you? in the context of all the other murders on the show, this is pretty serious. way more serious that the waiter in AC or any other random civilian who gets caught in the cross fire.
i know chase leaves things hanging out there (i.e. Furio, the russian in the woods) but this is a little more important. and very close to home.

it is a a very deliberate decision by Chase to not follow this story line in an obvious way. WHY do you think Chase does this? instead he toys with us, providing motive and method. Then he leaves subtle clues. he flips the hummer. he even throws in a cat to stare at the picture of CM.

still no one has commented on why CM does not want an ambulance after accident.