They used that very premise to make a movie: "The Day After Tomorrow," starring Dennis Quiad. They had New York flooded to the waist of the Statue of Liberty and the lowland swamp that is present day DC was still dry (go Figure).
Maybe it can happen, maybe it will happen, but you know what? If you aren't prepared to survive you won't. End of Line.
Surviving any disaster is a matter of chance and preperation. Knowledge is preperation, food storage is preperation, substainable living is preperation, choosing a location is perperation, and if a person is smart (I'm at least not dumb) they are doing all of those things.