While clear and concise language is preferable over that which is vague and/or ambiguous it is no guarantee a company still wont make the attempt and simply let the union grieve it.
Your cited Force Majeure case involving SARS at NWA is a perfect example -
NWA laid off thousands of mechanics, just like all the other airlines, citing the Iraq war. NWA then tried to add another 150 or so mechanics to that list citing SARS.
AMFA took both layoffs to arbitration - they lost the Iraq war Force Majeure, but won the SARS portion, and those 150 or so mechanics came back.
By all means, strive for the best language you can get, but dont for an instance believe it'll stop the company from trying to stretch things if they think they can get away with it.
Pilots, who arguably have had better language than most mechanic agreements also were laid off at NWA when they tried citing SARS Force Majeure.