If the airline states "crew missing" as a reason for a delayed or cancelled flight, the airline is not blaming the weather or some other force majeure. Exactly why the crew was missing will not be explained by the airline. The crew being drunk is unlikely, the captain being sick would be more likely, but the airline would - for many reasons - not go in the such detail.

Another thing is that delay reasons has it own set of rules. If a flight e.g. ARN-LHR is delayed due to weather at ARN, the delay code is "weather". If that delay will delay the return flight LHR-ARN, the delay code for the latter flight isn't "weather" but instead "late incoming aircraft". If the aircraft and crew were suppose to continue ARN-SDL, but can't because of crew rest rules and no stand by crew is available, the cancellation code for ARN-SDL is "crew missing".