So Riot is there Any Skins that will STAY Limited?

So a bunch of skins have been staying in the vault so i was wondering what you are planning to do with rare skins like pax ones. Are you planning to re release the skins again or is the pax events i went to special because a one time skin i got from it? I love these skins and the uniqueness that they provide to my champs. What are your plans for rare skins in general? Will you keep some of them rare or will there always be some time that they come back.