FFF
You have just asked the million and one dollar question with no correct answer.
Depending on what the intelligence actually is/ the source of information / the reliability or credibility of the source/ the corroboration that may or may not be available to the intelligence will make the difference to what action you take in this situation.
Even when you make the correct decision the conspiracy theorists (aka the terrorists best friend) will give you a hard time and jeopardise any similar decision you may have to make in the future.
For what its worth I think that if you have not identified the persons involved you cancel the flight and hope the intelligence improves on the next occasion. Remembering that what ever action you take, will influence the terrorists next move and may also disrupt the flow of intel you have.
The ultimate no win situation with a very big 2nd prize
Cheers
Ice