[Flaming Fist Enforcer]

Well, as you don't have to go back to CK, you don't have to worry about it. Forget it and get back to playing.

You can kill ALL the guys who work for Sarevok without ruining the plot. You can let some of them go, but killing them won't change anything.

There's also noone waiting outside the CK's walls so you can just proceed to BG. There should be someone waiting for you in all the 3 places you mentioned. However, you won't be able to reach one of them before you visit the Undercellars.