Rat drop procedure on 604/605 is fully supported by a FCOM in flight check procedure so can by conducted without any special flight release, although it does call for VMC. An engineering visual inspection prior to in flight deployment check is required on certain units, in which case normally prevents a drop on the way into mx.
If the event on landing was due to electrical issues, they possibly didn't restow the manual release handle which can apparently cause 'damage' to the electrical control system and/or prevent switching of the essential bus back to a gen prior to landing. During my involvement with this check, despite a pre-brief, i've often had to remind crews to restow the deploy handle even when they're running the list. I guess it gets lost in the awe of the RAT noise and unusual cas messages
I wouldn't be suprised if the procedure is revised to further reinforce this important step in the near future.
I'll be very interested in the investigation on this one.