Is it possible that he died at sea, body not found ?
Is it possible that he emigrated and died in another country ?
The date on headstone might be incorrect.
I found one date on headstone that was out by 100 years, 1849 should have read 1949.
One grandfather of mine is on death cert as a farmer, but he was a builder, who kept one cow to provide fresh milk for family. The doctor was informant.
Have a look in local papers around date, you may find obituary.
Good luck with the search