Being that Cartier is considered "the Jewellers of Kings and the King of Jewellers" as they have been servicing royalty for a long time, I have never been concerned of diamonds or gems falling out of any of their creations.
It’s not that it can’t happen such as a rare faulty setting or hitting the item on a hard surface and the diamonds falling out as they would with any brand, but being that they are Cartier and one of the most prestigious jewellers in the world, the chances are highly unlikely.
I have had the Cartier Destinée wedding band in PG for many years and have never had an issue with it (even the one time my cat decided to take a bite on it! LOL - luckily, I can’t find any teeth marks on it).