Once they locate the wreckage, if the weights aren't nearby that's a strong sign they were detached before the implosion. They would have fallen to a different location on the seafloor than the hull because they're denser and have a smaller cross-section, thus not affected as much by the hydrodynamics during the fall.
I thought the drop weights were held on by electromagnets--essentially a dead-man switch kind of fail-safe. So therefore when the power failed due to the implosion the weights would drop.