So a decision is taken to balance the fuel, the crossfeed cock is opened and the respective pumps switched off but the fuel tank page is left displayed. As we all know we are human and only need something to distract us to wind up draining two tanks at an inappropriate time. You don't get a fuel assymetry warning as they drain down at approx the same rate.
I would be very surprised if that happened, fuel balancing is not encouraged at BA and i've never seen it done at that kind of stage in the approach. Turning main pumps off is more or less a no no. Also the Boeing would generate a fuel low tank x eicas long before it ran dry.