I don't expect them (BA) to give up a single slot at LGW.
I'd beg to differ. Whilst I would be surprised to see a complete pull out from LGW, there's no doubting BA will have to resize and restructure their network. Apply that same quote to LHR and would be in full agreement I'm sure with many others.
If that means they move the likes of Bordeaux, Seville, Verona or on long-haul Orlando, Antigua etc. as well as consolidate others (ie FCO, NCE) at LHR to maintain slot position there, I'm sure they'd do so. They have to protect their slot portfolio at LHR, there's virtually no doubt of that.