And what if the planned emergency landing (say at KEF for example) has to be abandoned because the airport is closed due WX or an obstruction on the runway? Assuming for a moment that some passengers/crew survived a landing on water in winter off the coast of Iceland/Greenland in winter, how long would they last in the water? As an earlier poster pointed out, hypothermia (and exhaustion from the high waves) would set in rapidly, probably before any boats/helicopters could reach them.
Landing on a beach near the Comores on a part of the Indian Ocean (one of the warmer bodies of water around the world), is one thing. Ditching in the north Atlantic in the middle of winter is entirely another.