It would probably take well over a year for the airport to be sold and for contracts to be exchanged...
Hopefully the expansion plans will be well underway, by then?!
Maybe BAA could go full circle and purchase the lease for LTN, with all that money they now have in the bank with the sales of STN and LGW. That way they would get their hands back on a second London Airport, but this time by organic growth.
Luton could attract a very hefty price tag to continue the contract with LBC, purely because of the shear potential from the airport. Having plenty of spare capacity which is a rarity for the London Airports and a council owner that is eager for growth... The airport could also offer to renew it or extend the contract to the owner.
Also any new owner is going to be keen to maximise their investment, so hopefully expansion would be at the top of their priorities!
It wouldn't surprise me if the Northern Ireland Assembly did something similar to Belfast International as the Welsh have done and wanted to purchase the airport. They are very keen to grow Long Haul traffic from the province, and have proposed to scrap the Air Passenger Duty.