After that, again
AFAIK, the long term plan is then to demolish and rebuild LHR-3, re-aligning it to make better use of the space available.
From what I have seen, T3 won't be rebuilt, but will have some modifications to clean up the layout. Pier 6 (the four new A380 capable gates) will extend slightly westward to allow six gates. Pier 7 (the control tower pier) will be demolished and rebuilt north-south, with access under the apron. This was all 'long finger' though.
I've also seen a conceptual drawing somewhere, with Pier 6 extended eastwards, to merge into the south facing gates of the new T2. Similarly, the north facing gates of the new T2 (phase 2 - replacing the existing Irish gates) could merge westwards into T3. This would create a ring of gates right around the CTA. But I'm not sure this was an official document.
Then there's a third satellite for T5 and a second for T2 also in the long term plan. But without the runway capacity, would they ever be needed?