In addition to the above, you really don't know where to look. With ANY sort of current and a reasonably buoyant diver, that person could drift a very long way. When a diver died during the U-Boat search described in Shadow Divers, his body was discovered purely by accident about 5 miles from the site of his death. The odds of finding the diver on the bottom are therefore extremely remote.
In addition, if you do by some miracle find the diver on the bottom, the odds of a positive outcome are about nil. In the only cases I know of in which an unconscious diver was brought to the surface and revived, the surfacing process began immediately after the diver became unconscious.