Costumes should definitely be permanent, we got an official answer on Telegram ( and that's the reason why I did buy the subscription, actually ).
And to everyone who says the sub isn't worth it, actually it IS worth way more than you'd ever think. I'm making 75 orbs ( could easily push to 100) and 50 tears every day, not to mention the acceleration on rituals with a few levels in ritual berserker( 4 rituals/day atm, and counting).
I'm almost sure that I won't renew the subscription; but since I've been playing this game for free for one year and half, I thought I may aswell give Zepto 5 euros for once.
Now I'm really jealous, since Windows doesn't even have that subscription option