ovum,
Has anyone here been witness to anyone ruining or having their career affected by excessive consumption - directly or indirectly?
Yes. It happened when I was a fairly junior F/O to one of our Captains who was an exceedingly heavy drinker. He consumed a dozen bottles of beer and a bottle of scotch each and every night of his life, leading progressively towards 'brain death' (my term, not a medically qualified one). It came to the crunch on a flight that I was doing with him, where, in a terrible weather / terrain combination, he just peered straight ahead and tuned out from reality, necessitating my taking control and command of the aircraft. My instant command lasted all of 10 minutes after the appearance of the Chief Pilot in the cockpit, who, unbeknown to me was travelling on the aircraft. Perhaps it could have been covered up had it not been for the Chief Pilot's intervention, but a good thing that he was finally found out.
He was not drunk, but fully sober with a brain battered by many decades of severe alcohol abuse. He was a particularly sad case, being initially employed as a "bright star" from an English aerospace company and progressively degenerated over the next 15 years or so. He was terminated, and could only find employment as a toll collector, and even that he could hold for no longer than 6 months.
Regards,
Old Smokey