Don't panic, LHR isn't closing. No politician wants to regenerate the Thames gateway, which already has 3 airports (LCY, SEN, MSE), at the cost of turning the Thames Valley into a ghost town! What would be the point? That would concentrate MPs' minds a lot more than aircraft noise.
The airlines have invested millions acquiring slots, so they aren't going, especially those recently transferred over from LGW. The owners are building and rebuilding terminals, etc., so they too are spending the money. Too much investment has gone into it already and the infrastructure and the expertise is already there.
So, don't have nightmares!