Hey there, as of Monument of Triumph, partner items have been moved to the 'Legends' section in Eververse where they will remain until whatever licensing they have expires. That also means that likely, any item not appearing there has been retired. Partner items are not available in the focusing system. The Fortnite sets seem to be an exception, perhaps a different agreement covering those. The intention of the Legends page is that when all items are retired, it will be removed. So that sounds like things are there until they get removed, and things will not be coming back. However no one can really say for sure unless Bungie makes an announcement that things will return.