I’m not so sure about Charles but I don’t think William thinks he’s been chosen by god. If anything, he seems to have a pretty strong disdain for a lot of the ceremonial and ridiculous aspects…the photos of him on garter day for example he can only just manage to his his embarrassment at prancing around in the robes.
I think Kate would be quite happy with a life similar to her sisters, more money than they could ever spend, days spent playing tennis, shopping and having lunches. Weekends at the country home with the kids. The odd show up to a charity function or other, but no more shaking hands and boring engagements. Honestly I’m surprised she isn’t a secret republic campaigner
ETA - they wouldn't even really lose much status. They would likely still be seen as "royal" at least for a good few generations and would probably still have plenty of people pandering to them