There is a school of thought which says that BA might regard a no-R3 decision as being to their financial advantage. In that scenario, demand and supply become increasingly out of kilter, allowing the incumbent LHR carriers to increase their yields. With BA gradually increasing its slot holdings, it is clearly best positioned to take advantage of such a dominant position.
Personally I think this would be a risky strategy for BA, as we might expect the competition authorities to step in if BA sought to exploit its dominant position. Actually I think BA is already skating on thin ice, as some of its recent actions might already be attributed to having an over-strong market position.