Why isn there a permission to prevent users from erasing a vault?
In addition to your vault object, there may be other drawing elements in your file. The AutoCAD WBLOCK command can be used to export all objects except the vault to a new file. The result is no different than erasing the vault and saving the drawing. Therefore, it is pointless to prevent vault objects from being erased, as the same end result can be achieved easily using other means.
