Chuck was a necessary +1 after a -4 from the group. He gets Lee on the right path with Clemmy, and helps get your group to safety.
I don't really see why Chuck stayed behind though. It's kind of similar to the KenBen death. Why not just run away with the group, they were right next to each other.
Kenny could have capped Ben and ran away with Lee too (even though I get why he didn't.)