Once Constantine has gone I think the family will drop any pretence of having links to Greece - those almost obligatory holidays to Greece every year to see Constantine and Anne-Marie. Of course they will keep the titles but without any feelings of obligations to Greece (don't think the CP family they have any but C&AM do).
Personally I've always though MC tired quickly of the 'royal role' - no doubt she thought it would be like the wedding - big parties with all the rest of European royalty and tiara events all the time. Instead it meant being held accountable more than other rich socialites, getting criticism for not learning Greek and having to pretend about one of Europe's poorer countries (if you watch interviews where they are asked about Greece MC always looks bored to tears). I think after the novelty of the wedding wore off and she realised Queen Elizabeth II and her royal mates weren't coming round for dinner every week. Likewise she saw her sister Alexandra was able to marry and get herself and children a title to make them stand out without any of the expectations.
Aren't Tatiana and Nikolaos living in Greece these days?