What places will they want to see that you believe might be affected? The city will be all set with holiday lights and windows, the tree lighting will take place the week after - buses start running tomorrow and subways (at least in Manhattan) will be at least partly up and running. This is New York City and it will come back quickly - now if they were planning on outer borough travel or trips that might be slower to return. What hotel were they staying at? I would just cancel it and rebook somewhere uptown or midtown.