Glojo,
I would think the RAF would fly the Typhoon as their sole front line jet, while the Navy flew the F18; as far as overall arrangements for OCU setup etc. go, there was going to have to be one for the F35 anyway, likewise for an OEU, so I can't imagine it would make much difference if they are manned only by the Navy, likewise for the RAF and Typhoon squadrons.
By the way, if you were also wondering about how the RAF would fill the hole of no F35, then I guess the answer would be a few more Typhoons and perhaps drop the idea of scrapping the first 60. I'm sure there are a lot of student pilots, holding at some admin job for 2 years, that would be happy to hear there are suddenly going to be enough cockpits to put them through Linton and Valley, in reasonable time...