물 건너갔다 (go out the window)

건너가다 [v] cross, go across; To move from one place to another across a river, bridge, road, etc.

semi-polite: 물 건너갔어요 

>>This expression is used to indicate that something has become irreversible and difficult to accomplish.

>> Usually, the verb ‘건너가다’ means to cross a bridge or road. But, in this case, it’s used for crossing a body of water, which means there is no turning back. That is why the expression is mainly used to express that something is over, and there is a low chance of it being accomplished. 

>>In the dialogue, the expression is used to mean Yoon-jae’s chances of appearing on TV are near zero. And since this expression refers to something that has already ended, it is used in the past tense.