All in all, whether permission for expansion is granted or not, I suspect LCY is a relative cash-cow for an investor...whether it will realise the £2b price tag is, in my opinion, dependent on the liklihood of approval for expansion. An investor with a pessimistic outlook might look at £1.5b as providing a realistic return on the investment, an optimist might look at £2b and think that was a good price. In reality I suspect, if timescales go to plan before the planning decision, the airport will go for somewhere between the two.
The local council is supportive, so it depends who wins the mayor election. If it's Labour, the desired expansion would probably not be blocked. On the other hand, if it's son-of-Boris Zac Goldsmith, the Boris status quo may prevail (unless Zac is only anti-LHR).