Englishman in Amsterdam
The Orc Guard remains engaged until you defeat it. It is never bound to the Tower Gate.
Note: Once you defeat the Orc Guard you must discard it on your player deck discard pile (not the encounter deck discard pile and not back into your deck).
Rules P.10 Discard Piles
Each player has his own discard pile, and the encounter deck also has its own discard pile. Whenever a card is discarded, it goes to the discard pile belonging to the card’s originating deck.