Well, IMHO Prince Philip is going to have to wind down his public life at some time in the next five years. He will be 100 years old in 2021, if he is still with us. He is doing marvellously well now but I don't think anyone would expect a man of that age to continue performing hundreds or even dozens of public duties per year. Philip already performs a great many of these, charity lunches, military dinners etc indoors at one or another of the royal residences like Windsor and BP.
If Charles intends a royal family of just himself, Camilla, the Cambridges and Harry (and spouse) then the vast majority of Philip's charities, the Order of Norfolk Bird Watchers, Ye honourable Devon cream churners etc will have to do without a Royal patron as I can't see these being handed on. The most important will be, however and, as Charles's diary is jam packed now, the Cambridges and Harry will no doubt be the recipients.