The characters combine to mean “[the situation has changed to a state where there is] no saving [possible] anymore.” This “change of state” is key to its feeling of finality, whether serious or mock-serious.
没救了 (méi jiù le) perfectly captures a specific type of Chinese conversational drama: a blend of exasperation, fatalism, and humor. It's a way to complain or pass judgment with a theatrical flair that everyone understands is often not to be taken literally. A good Western comparison is the phrase “it's a lost cause,” but with a key difference in tone. Saying “he's a lost cause” in English often carries a heavy, serious weight, implying genuine concern or giving up on someone. 没救了, on the other hand, is frequently used between friends as a playful jab. It's a social tool for pointing out a flaw (like being chronically late, being a picky eater, or having a terrible fashion sense) in a way that is simultaneously critical and endearing. The underlying message is often “I'm so frustrated with this trait of yours, but I accept it because you're hopeless and that's just who you are.” It's a complaint wrapped in acceptance.
This phrase is incredibly versatile and thrives in informal settings.