"Destroyed" is a possible status of a survey mark. Destroyed can mean that the marker no longer exists at all, or it can mean that the marker has been moved completely out of its position.
No survey marks should be considered to be destroyed unless the NGS officially classifies the mark as destroyed. They are the final judge of the destroyed classification. They are quite conservative in this evaluation. For instance, even if the mark's location has been paved for a parking lot, the mark may still be under the pavement and the NGS will probably not consider it destroyed.
The NGS prefers the more optimistic "Not Found" unless you have direct first-hand evidence that the mark is completely obliterated or its entire mounting has been uprooted from the ground. Getting a mark listed as Destroyed in the NGS database requires submission of evidence (like a photo) and an e-mail.