In the writen story, the father narrates to the reader that they will try to drive out of the mist / keep going until they run out of gas. I believe he implies the shooting at the end by mentioning the number of shells left in the gun.
No, the story doesn't imply any shooting at all. They are simply driving south state by state filling up the car with gas from gas station to gas station trying to escape the mist. The story ends with the Dad hearing a short burst of what he thinks is a voice on the radio they have, implying that there is an area of the country not covered by the mist.
The ending of the movie was just straight lazy, retarded writing. A group of people do everything they can to survive and fight their way out, being extremely smart the entire flick, then get into the car and become complete idiots who immediately give up and become suicidal afterwards.
Who would want to stop and get more gas? Nah, let's just drive aimlessly and shoot ourselves instead!
I don't mind a negative ending, but the flipping of personalities and forced stupidity of the main characters was bad horror movie level.
This post was edited on 2/7 at 8:09 pm