It differs very much from country to country. Even in London there was no white-tie wedding party. In the Netherlands in 1966 there were a couple of white tie events (official banquet offered by the Government, pre-wedding ball). In 2002 however these were black tie.
In Monaco there was no diadem event during the wedding of Prince Rainier with Miss Grace Kelly. His son however had a white tie event. So things can change indeed.
As this is a jewels message board, of course I hope on lots of sparkling as well. The most important however is that this is genealogically and historically a very interesting match. I wish the couple the best for their future.