cr:5.4.3a

If a meta-static ability that modifies rules outside the game ceases to exist during a game, it does not affect the legality of the rules followed outside the game.

Example: Shiyana, Diamond Gemini has the text “You may have specialization cards of any hero in your deck.” If the player controlling Shiyana has specialization cards in their card-pool, and Shiyana lost this meta static ability during a game, having specialization cards in the card-pool is still legal.