I've rarely (almost never) seen someone lose a contact while scuba diving.
However, I just opt for prescription lenses since you can't lose those and if I lose the entire mask, I'd be in the same boat either way.
True, but in the rare event you lose a contact lens while on a dive, it's easy to replace a lost contact lens (provided you are able to see well enough to end the dive). Keep spare lenses in your dive bag, and just pop a replacement in your eye once you're back on the boat. For the price of a prescription dive mask, I can buy a 6-month supply of contact lenses.