if an organisation is keen to stop people walking out the door
You are assuming this to be the case - a PVR is far cheaper than a redundancy (and remember there were no qualified pilot redundancies on the first tranche). In theory, you still also have the individual to fill a non-flying appointment for 12-18 months (albeit on a "work to rule" basis
). The financial penalty may be just enough to keep those who are "undecided" as to where their future lies stay in. I suspect those determined to leave will go regardless.
It is however a very dangerous game to play and one that could go horribly wrong (for the MOD/RAF) if they have misjudged the true feelings on the shop floor. Which I suspect they may well have done .....
Edited to add - latest voluntary outflow stats
here