The other problem the RN may have is that if the RAF walked away from JFH tomorrow there would be a (significant) manpower problem. There are a lot of Dark Blue 'appointments', at most ranks and almost all, if not all, trades and branches that are either gapped or filled by Light Blue. The manning is certainly not a 50/50 split (as was originally envisaged). Last time I looked it was more like 65/35 split in favour of Light Blue.
As discussed on previous threads I think both GR9 and GR4 will take hits - most likely, IMHO, is that they will both be drawn down quicker / steeper / earlier [take your pick of one or all of the options] than previously planned (despite signing of recent support contracts which will almost certainly have a +/- figure on target output requirement to allow for such things to happen).