Well, I am of half a mind to point out that any "new" airport will not be an overnight mushroom and will take 10 years in then planning and building. So, it is arguable that will give folk time to work out travel and other patterns.
The 10 years will almost be as much as it will take any new runway to be built. As there will have to be fresh planning permission for a start, a public inquiry, a hybrid bill for the inevitable land snatching and a more than inevitable trip to the ECJ in terms of how the new runway will affect various directives (after the domestic appeals process has been exhausted first).
So if a government was to bite the bullet then it would recognise that Heathell would inevitably shut (BAA trousering a fortune from the development of the site) and start consulting widely on where a nice 4 runway with room to expand, closeish to London and with suitable transport links could go.