I haven't heard of any ending date at all, and I can't find anything resembling an event page for the Garo crossover. Most speculation I've read was that the event was continuing, since it's more so just Garo-themed gear and mounts that are earned via achievements. And the gear is purchasable with Wolf Marks. It's not really like Yokai where the event items had to be bought with FATE drops.

The achievements aren't under the Seasonal achievements tab either. However, I'm not in-game at the moment so I can't check to see if the Yokai achievements were also not under seasonal. Not sure if that has anything to do with if the event is a permanent one or not, though. I have 4 more sets to finish to be done with it, but I'm hoping it's here to stay. i know the gear is purchasable with MGP and all, but some of the pieces are good glamour pieces. The fact that their durable makes them even better.