Do as your told, why be a hero? Nothing to be gained at the end of the day!
So lets say the hijackers want you to fly into Canary Wharf!
This was all over in about 20 minutes, so you squawk 7500, and then what?
Who's to say your hijacking won't last longer. An Apache pulling alongside you, would put a few extra thoughts in the minds of the hijackers.
Get these people nicked on your account and pi$$ them off and you would be looking over your shoulder for a long time.
How are they to know it wasn't a genuine emergency? Unless you go spouting off to the press etc how you thwarted the hijackers plans!