I think EI will retain at least some form of presence in T2 for now. They have just spent a lot of money on a lounge there. A lot of flights would have to be moved out of T5 to accommodate EI's entire LHR operation. Also, EI being in T2 serves IAG's interest to an extent as it means they can easily keep tabs on what's going on there, just as BA used to at T3 when it had one route there (MIA).