I wouldn't say Heathrow is "dead". It will never be dead, but it will become increasingly unsatisfactory and unpleasant as more flights, more people and more terminals are shoehorned into the same area.
I'll probably get shot down in flames for even mentioning it, but I don't understand why the possibility of moving lock stock and barrel to Stansted has never been seriously considered? I know you'd need to build at least two new runways and a couple of huge terminals, plus all the infrastructure, but at least it could be purpose built for the most part.