From the Guardian: Heathrow's Terminal 5 launch not so good: T5 launch marred by delays and cancellations . Problems included a failed baggage handling system (a software problem), and flash mob protestors. The cost of the terminal was £4.3 billion ($8.6 b), which is pretty amazing, I mean, you could build 10 stadiums.
From the Times:
Cancelled flights and baggage chaos mar Terminal 5 opening
And from the Telegraph:
Heathrow Terminal 5 flights cancelled amid luggage chaos
From the Independent:
Disastrous opening day for Terminal 5
This has been controversial, and issues remain about runways, but clearly some of the terminals at Heathrow were obsolete; the question of "what is to be done" included encouraging traffic at other London airports, though Heathrow was the most convenient by far, with a stop on the Piccadilly Line.