When one diver is panicking and can't be helped, that, unfortunately, is the time to kick away.
In shallow open water, even with a panicked diver, a rescuer might be able to position themselves above and behind the victim, grab the first stage and back of BC and then kick to the surface, dragging the victim with them. If the victim were in a total state of panic, they might not even realize that they are being dragged to the surface.
Of course, having an operable LP inflator functioning on your BC would be a huge help (which it sounds like was NOT the case for the survivor).
Conceivably, if a rescuer was small and weak and two divers were struggling so much that it appeared too dangerous to approach them, it might be possible to back off and literally wait until they drown. Life guards are taught to do this, if the victim is struggling too hard and is unmanagable, it is better to back off, let them exhaust themselves and move back in when the rescuer is confident the victim no longer presents a significant threat.
Once the divers had stopped struggling, it would be safe to approach them, remove lead and or gear and then send them to the surface by inflating their BC's or dragging them up or some combination there of.
I'm not sure the people involved in this accident had the ability to function in this manner because they seemingly failed to perform other, simpler actions (like dropping some lead and swimming up), but if someone were determined to try to help in a really bad situation, "backing off" might be a better response than "finning away". Running to the surface to "get help" is not very likely to result in a desirable outcome, in this situation the victims were not found until an over night soak.
A very sad situation.