I think we are saying the same thing, basically. Essentially there does come a point where the search is effectively concluded. I have had too much experience with these kinds of events and to this day the books are still open on some of them.

Most poignant to me is the still unresolved disappearance of Paul Fugate, an NPS Naturalist at Chiricahua National Monument, AZ, who went out to check the nature trail on a slow Sunday in January 1980, and hasn't been seen since. We mounted an intensive operation,, air and ground that lasted more than two weeks in the intensive phase, but that then tapered off, although not quite concluded for several months. In the tapering phase, we conducted searches of nearby mine shafts and adits, acquiring some very useful and rigorous training and experience. To this day, nothing has been found of any substance and contending theories abound

I had worked with Paul from time to time, the last occasion being about two weeks before his disappearance, and we had many mutual friends and colleagues.

Of course, many of these cases are eventually resolved. There was the abrupt disappearance of a backcountry ranger in Sequoia-Kings NP some fifteen (?) years ago. His remains were eventually found after roughly three years.