I also don't agree with characterizing this couple as "cavalier" - we don't know that.
There are legitimate reasons for missing a life boat drill - and illness is one of them. Many drills are held before the ship sails away. What if you discovered you had left your medication in the taxi and you had to make an emergency dash to the pharmacy at the last minute. It does happen.
What if you had food poisoning and really couldn't leave your stateroom? (because you had to stay close to a toilet).
Then would you have to leave the ship because of zero tolerance? Did the new CLIA guidelines outrule "make-up" drills? (I don't think so).
No - the prevailing opinion seems to be "you should go to the drill or expect to be kicked off the ship."
No exceptions? No second chances? No "personal service?" -- remember, as I said, this is not a "law," it is a cruise line policy. The cruise line has the full discretion to make an exception.
Now, I don't know where we stand now. Some of you may think I am picking on Seabourn. That is not true. Nothing would make me happier than hearing Seabourn has resolved this matter amicably. And if they do then they deserve full credit for handling it properly.