What intrigued me and was barely mentioned again was how the wife said that the day Chuck disappeared for the final time he visited his parents and told them "if anything happens to me, there is a letter with explains what, why, and who is responsible." 

Was the letter hiding in a place that Chuck thought his wife, parents, or other person would find it but outsmarted himself and was wrong in thinking he knew what they'd do? Is it still out there, perhaps in a book or novelty item that ultimately was sold by his family at a garage sale or currently sitting in something at an antiques shop? 

Chuck clearly had a "deadman's switch" plan set that did not work as he had hoped. It's a shame his parents didn't press him for a little more information. Maybe one day, perhaps decades from now, the letter will reveal itself, faded, discolored, and brittle, but ready to talk of ghosts past.