As far as I know only 2 crossovers have been retired and their items put in the shop: the first FFXI and the FFXIII event. Personally I would rather they bring them back from time to time, like all the others. They have have so many exclusive shop items at this point, selling event items won't be missed.

Repeating holiday events or allow people to chose to replay them comes with certain complications when it comes to group content.