If it cannot be destroyed or vendored, you just have to keep them in your bank. Not a lot can be done unless Blizz makes a change. I notice on the Core and the Wish, Wowhead has them with a vendor price, so I don’t know what is up with that, I know the Heart cannot be destroyed and because of unique, they cannot go in VS. /shrug
Now this I support! I’ve got the legendary ring, cloak, many from legion, and other things I just can’t part with. My ammo bag and quiver that took much work to get when they were current. Currently the only items in void storage are gear sets that are in my mog collection anyway.
I still have my Core Leather soul shard bag, all three items to summon the dreadsteed, the urn for Kara, the Scepter of the Shifting Sands, and a few other odd things that are no longer in the game.