Biggus,
By that logic how many AD Sqns do you need for a very occasional QRA? As with disaster relief, when you need it you really need it.
I don't think SH is that bleak Crab; I'd assume one of 28/78 will become a third CH47 Green Sqn with the Mk6 arriving. Maybe the other numberplate will become a joint CH47/Puma OCU? I reckon we'll lose one numberplate if it's managed carefully.
SH numbers are not going to be squeezed by UCAS over the next epoch, unlike manned Combat Air, so, who knows, maybe after a couple of obligatory Typhoon types next there could be a FJ mate with Pred/Reaper high in his/her competancies?