SS,
So you have answered 1 out of the 5 points set in your homework task, with a ludicrous suggestion that low costs airlines would want to use such a high cost airport.
You get 0%
As as for sellling off LHR, there really isn't that much space to sell, considering how compact the site is for such an important global facility. To suggest it employs such a low number of people per acre is ridiculous.
Just to clarify - who actually owns the land LHR is built on - is that owned by ADI, or UK govt? Either way, any land around the airport which is used for airport related activities is still private.