I moaned to Tripit about there being no notification of the disappearance of the flight and got a reply which said:

"While we don't send travel alerts via email or SMS alerts when a flight is pulled from the schedule, it sounds like we need to improve the monitoring status within the itinerary as well and possibly alert you when a 'once monitored' flight is no longer valid."

What on earth is the use of the service if they don't do that?