I think Anne and Charles are the closest of all the siblings, and of course she will continue to support her brother once he is King. Her nephew too, if it comes to that. I could see her following in PP's footsteps, gradually tapering off her duties, passing on her patronages, and retiring at 95.
The BRF definitely need Anne.
The Kents and Gloucesters will be too old once William is King (I think they should retire under Charles).
That leaves Charles, Camilla (who also seems to have health issues), Edward, Sophie and the Cambridges.
At least until the Cambridgetties are old enough Anne, Edward and Sophie need to stay on.