I have not seen any type of special evening party or special dress events on any cruise / line I have sailed. Cruise casual is typically the norm, thanks to tired or awe-struck and confused guests - and the possibility that luggage may not have been delivered to cabins before dinner. (That’s rare, but it does happen).
Ditto, the last night. Luggage gets out in the hall - you don’t want guests skipping an event to pack their outfits.
The trend is a lot of cruise casual, throughout a cruise. Pirates are rather casual aren’t they?