I would think its safe to say that the 747 route network is pretty much set in stone now until retirement.
I would think at the earliest opportunity BA will look to get the 747's off routes to SA and West Coast USA once they have something that can replace them seat wise... obviously no more 380's and 777-300s in pipe work at the moment.
I would however suspect though if BA fill those planes to those destinations as they do atm hence the extra CPT service then maybe they don't see it as so much of an issue ?
Be very interesting to see what the 350 gets introduced on to and the continued development of the 787-9 network.