We loved the PG too, that having been "our" restaurant on two of our times on board. It's bar, on One Deck, was a hidden wonder and open to non Grill passengers too, it was a favourite starting point to the evening for us, it was wonderful!
Both the PG and BG are still there, the Britannia is currently being used as a restaurant for the staff on board, we didn't see it, but there are plans for it, maybe as a specialist steakhouse. The Princess Grill is being worked on, we understand it's Race chairs are all shrink wrapped and in store, the statues are still in place and protected by plastic.
Some of the restaurants are being offered to third party operators, including the Caronia I believe, it may also be divided into two, but I can't be 100% sure about that...