I gave a beta key from my Kickstarter pledge to someone, but never intended for that person to have the full version of the game.
Since Larian's default policy of key expirement changed into beta access == full game, I used the Larian Vault to destroy that key and get a gog key instead.

Now I got Divnity Original Sin on gog, and the Steam key has dissapeared from Larian vault, but my friend there claims he can still play Divinity with the key that was supposed to be unvalid. It may be that the key is not made unvalid at all, or perhaps that it will only be so once he tries to reinstall the game.