It doesn't look like he's buried with his family, does it? They seem to have a list of all the burials:
http://quakertownonline.net/Old_Rogerene_Cemetery.htmHave you found Lydia in 1860 without David? For reference, here is David and family in 1850:
https://www.familysearch.org/ark:/61903/1:1:M68T-JJ8Can you get access to this collection:
Connecticut Deaths and Burials, 1772-1934
https://www.familysearch.org/search/collection/1674748On a typical search for deaths in Connecticut, familysearch says this about that collection:
Images Available
To view these images you must do one of the following:
Access the site at a family history center
Access the site at a FamilySearch affiliate library
-- HIre someone in Salt Lake City to look for him?
My first thought was that he died at sea, but Griswold is far enough inland to make that unlikely, and on the 1850 Census David was a stone mason, so that option is probably out.
Could he have returned to England for some reason (e.g., death in the family) and died there?
I only read that page about the cemetery quickly, was it all Quaker? Do Quakers restrict burials in their cemeteries to only Quakers? Was David a different religion from the rest of his family? If all answers are yes, is David buried somewhere nearby?
-- Hire a reseacher in that area to look through the other cemetery records?
Have you contacted the town and or state and asked them to do a search for David? When I was researching in New England, the town was usually cooperative and was also cheaper than the state. In New England states, the county does not have the records, just the local town/city and then the state.