If you ask me, there's very little the 787's can do in the VS network that the A330ceo can't do. And when the neo's come along they will theoretically be able to fly anywhere on the current network. It's probably one reason amongst many why they went for the A330neo instead of ordering more 787's despite the merits of moving to a two-type fleet.
The A350's on order that are to directly replace 747's were due to be configured in a higher density layout to the first few A350's operating out of LHR anyway.
In any case, if VS does survive I can see merit in consolidating London operations out of LHR given there's probably going to be slots freed up as a result of a downturn.