Should William die while still The Duke of Cambridge, Kate would immediately become The Dowager Duchess of Cambridge but would almost certainly still be called The Duchess of Cambridge until such time as George - the new Duke - married.
But with William out of the picture and The Queen unlikely to survive another 20 years, George would be Prince of Wales by the time he married, or even King, in which case Kate would remain HRH The Duchess of Cambridge for the rest of her life, unless she remarried. In that case, since married women are still treated as nothing more than an extension of their husband when it comes to their formal identities, particularly in such rarefied circles, Kate would be known by whatever name tradition dictated as appropriate for the wife of whoever she married. However, it is likely that Charles would cook up some new title for her or at least let her keep the HRH since it would probably be deemed inappropriate for the future king's mother to be known simply as Mrs John Smith, though HRH Mrs John Smith sounds even stranger to me.
Though, of course, she would be likely to marry a peer rather than some ordinary bloke, so might become, e.g., HRH The Countess of ..............
I think that would be the position, anyway. I may be wrong, in which case I am sure someone will tell me.
nw dare you, like the pippa gets her mail, this is Pulitzer worthy
I can't wait for the next article. I am certain we will learn they plan to wrap gifts in shiny paper for each other.
