What should I do if World of Color gets canceled?
This happened on two nights in the first summer of 2010 and caused a great deal of guest relations problems for Disney as you might expect. Most likely if you have only a FASTPASS you are out of luck, much like any other Disney attraction. If you had a preferred viewing spot because of a dining reservation you should make your way quickly to guest relations (because the line will be very long) and ask for FASTPASSes for a future show. They may or may not give these out, but for some people in 2010 they did.
See
this thread for DIS posts about the night all three shows got canceled.