Most of the Sea Harrier pilots that left were going to do so anyway, either due to having done their time, or getting to the point that the move wasn't worth it for the few months they had left in the RN.
I don't think there's any masssive hidden plan for the RAF to take over the Fleet Air Finger, it was the RAF that gave up half of it's jets to the Navy. Unfortunately, it has been obvious for quite some time now that the Navy were going to be unable to man it's two "new" sqns.