The "Bound by honor" objective says that if all triangle units are allied to players you can discard the objective to gain one dragon rune. Last night I was playing and suddenly the triangle neutral units all were defeated. There was no city to place triangle units on the table.
So was the objective accomplished or not? Is it impossible to accomplish the objective? If so does the player just stick with his impossible objective. It would seem that it is still possible because contrary to other cards (giants and dragons) the card doesn't say that if it's impossible to achieve you get to discard it.