A lot of people complained that this episode was too dark and I can see why. For starters, the alien itself was just a shadow and I don't know if they purposely did that or if this is the same FX crew from GoT who are going for TVs that support full black displays or some other weird shit I can't imagine.
I don't think the Sheriff is dead because why hire an actor with the pedigree involved, I am sure this isnt the last we've seen of him.
As for Ahmed its all setup quite right isnt it? First, he does the thing that makes his wife hate him and eventually he's going to die and they'll find something else about the aliens as a result of it but hes also going to have one of those epiphany moments where he gets redemption for all hes done. Either ways its moving in that direction as I think the aliens aren't killing people just infecting them slowly.