If the ability triggers and the Urn isn't sacrificed (because it left the battlefield or changed controllers, for example), the exiled cards won't be returned to the battlefield
MTGNexus homepage MTGNexus creator options Pros: Layouts for every card frame you can think of Save cards as sets, cycles, or individually Great forum for discussing card creation topics Collection tracker tool Cons: Requires sign up How Do I Print My Own Proxy
Do All Giants Have Reach
That being said, this allowing you to potentially get a crazy amount of stats on board for a short time, and this might be a nice way to enable you to win over the top with some light burn
Geralf, the Fleshwright creates a Zombie token when you cast any spell that's not your first spell that turn, Open the Graves creates a Zombie token when a nontoken creatures you control dies, and Cryptbreaker makes a Zombie token by discarding a card and tapping itself
She's super flexible because of her Partner ability, letting us add almost any colors we want to her identity