EC 261/2004 applies in this case, so Norwegian would be obliged to provide an alternative transport and depending on the reason of the cancellation, possibly also compensation. Plenty of alternative ways to get from JFK to ARN, though they may involve connections. I wouldn't be too worried but of course it is possible that some icelandic volcano decides to blow some ash into the atmosphere again and shut down all Trans-Atlantic air travel for a week or so.

http://europa.eu/youreurope/citizens...r/index_en.htm