I do agree it should be easy to flag a card "do not serve" for a certain number of hours. It would be easy for the cruise lines to implment (from an IT perspective) and it would yet another way for the cruise lines show the public they do care about people.
However, it is merely a gesture, since people CAN smuggle drinks on board, steal drinks or get others to buy them for them.
If the family is indeed just asking for $15,000, then their strategy appears to be " just give us the money, its cheaper than a trial" however, that probably comes from the fact that cruiselines often settle all kinds of cases.
At some point, the lines are going to get like some other companies and say "no more, you want money then sue us." That is the only way to get rid of the notion that an industry is an "easy target".