There are three different years stated for his death, but unlike Josette or Naomi, all of them can actaully be expained.
1. His original year of death as stated by Prof. Stokes upon meeting Barnabas and Julia was in 1830. He got a parcel of land and educated himself and he prospered, had a family and died peacefully.
2. In 1897, his headstone states he died in 1816. His year of death changed becasue he had the deaths of nathan and Natalie on his conscious for the rest of his life. While now he may not have been given his own land and prospered, he remained at Collinwood. Though he still did marry and have a family of his own. Joshua probably did reward him for his loyalty in some way.
3. Following the final 1796 flashback, Natalie is bit by Barnabas and under his spell. Most likely, she never did bail out Nathan Forbes. So, neither were ever killed by Ben Stokes. He doesn't have any deaths on his conscious and now lives to 1840. He still probably lived at Collinwood and without the stress of owning land he lived 10 years longer then he opriginally did. Once again, he still married and had a family of his own and Joshua may have helped him out in someway.