If Theater of Horrors leaves play, can the cards exiled by it still be played?
No, because you won't have the static ability "... you may play lands and cast spells from among cards exiled ...."
604. Handling Static Abilities
604.1. Static abilities do something all the time rather than being activated or triggered. They are written as statements, and they’re simply true.
604.2. Static abilities create continuous effects, some of which are prevention effects or replacement effects. These effects are active as long as the permanent with the ability remains on the battlefield and has the ability, or as long as the object with the ability remains in the appropriate zone, as described in rule 113.6.
Private Mod Note
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Rollback Post to RevisionRollBack
Why bother with mere rulings when so many answers can be found in the Rules?
And to clarify further: if you play another Theater of Horrors, even if it’s physically the same one that was on the battlefield earlier, you won’t have access to cards exiled by the earlier iteration of Theater, as the new Theater of Horrors is a different object and unrelated to the one that had exiled those particular cards.
No, because you won't have the static ability "... you may play lands and cast spells from among cards exiled ...."
Commander/EDH Decks:
BRG The Blood of Jund - Kresh the Bloodbraided BRG
WR The Blades of Goldnight - Gisela, Blade of Goldnight WR