[user104658]

Well there are really only two possibilities... one is that something happened to him, the other is that he does not WANT to be found, which would be the only explanation for going completely off-grid. It's not entirely unheard of but I'd say unless there was some previous indication that this was something he would do then it does unfortunately seem less likely. More plausible if he'd previously expressed a desire for that sort of existence.

It's really hard when no closure is available, sadly it happens a lot. A past colleague of mine's nephew has been "missing presumed dead" after jumping from a bridge into a river. Witnesses on the bridge saw him jump, it was a large drop and the water was freezing (December weather) however despite 999 being called straight away, a body was never found. That was about 5 years ago. As I say logically there's no real chance he somehow survived and has been in hiding for years, but so hard for the family to move on when they had to have a funeral with an empty coffin.