While I personally agree with Moose Bob (the moderator) that in cases like this NA should be used I've held back, gone with the majority, and only posted a NM.
This is a cache that I walk past many times a week and I know exactly where it was. The unique feature of the tree that this cache was in has been removed, not altered, removed. There is quite literally nowhere on the tree that remains to hide a cache any more. In my opinion this is a clear case where NA should be used but because of the general view here and a friend of mine pushing to keep me from archiving it I've backed down and gone with NM.
The problem with NM, in my opinion, is that the cache is gone. I know it's gone, there's no question. Why should such a cache (it's not even a cache any more, it's gone) be left on the map when there's no chance that I'm simply missing it or that it's been moved a bit? As has been said, archival doesn't need to be permanent. If I have a cache archived because it's truly missing and the CO goes and replaces it the listing will be reactivated. It's not as if a cache being archived is a judgement on the CO, sometimes caches simply disappear (then again I think that more people should post DNFs but everyone seems to be to ashamed to, maybe it's just me).
So, I'll leave this marked as NM for 24 to 48 hours and if nothing is done or the CO doesn't at least post a note I'll post a NA. The only reason that I'm waiting as long as I am is the CO has been active within the last day and nearly everyone (minus myself and Moose Bob) seems to side with the idea that NM is more appropriate.
EDIT: Fixed grammar.