However British Airways must be feeling quite confident about operating their leisure routes from Gatwick in competition with Easyjet. I say this because at the moment it is BA introducing the routes in competition with Easyjet and not the other way around, as has been the case in the past.
As for Easyjet at Heathrow or the 4th runway, they are both about 10 years away (if ever). Plenty of time still make money at Gatwick. And if Gatwick should get the 2nd runway rather than LHR its 3rd things could become very interesting.
v.