Now I'm sure they have contemplated what would happen if Curiosity actually found water. After all, it's looking. The Mission Planners would have to take that into consideration, of course.

Curiosity would be amphibious. I'm sure it is. I mean, what if it found A LOT of water? The electronics would be waterproof, able to function even if underwater. Only makes sense. Duh! Remember, it is actively seeking water.

The wheels would act as paddles, able to go fore or aft, or even sideways. It could turn on a buoy, though if it found a buoy that would be pretty scary.

I don't know how far Curiosity could get, but I'm assuming it could make it to dry land, or maybe moist land, and keep it's antennae above water.

Remember, these things are expensive, and one must plan on finding that for which one is looking. And then one must consider the contingencies. After all, NASA isn't stupid. They built the Space Shuttle and ISS, for instance.

I shouldn't have to explain all that.