Imagine Malekith and Kurse don’t kill Frigga but kidnap her and then try to ransom her against the Aether. Odin thinks he will only see Frigga again if he is prepared for the world to be turned to darkness. He thinks little of sacrificing Jane though, which maddens Thor and turns him against his father.
Loki has no reason to help Thor, but he sympathizes with Jane and besides, he has developed a personal interest in the power of the Aether. So he casts a spell to pull the Aether from Jane’s body, only to find that his magic isn’t enough (which may be just as well as he was thinking of absorbing the Aether himself).
Meanwhile, Frigga is being a terrible hostage. She can’t escape but she can still make her captors’ lives hell. Their ship’s instruments show incessant reruns of Midgardian cartoons, the lights won’t switch off anywhere and the elves can’t sleep. Then they start finding Frigga everywhere - multiple Friggas - and don’t know which is the real Queen and which are their crewmates transformed into her lookalikes.
Like in the film story, Thor, Loki and Jane go on a quest to Svartalfheim, only in this case with Odin’s hard-won approval. By combining forces, Loki and Frigga trap the Aether before the exhausted Malekith can absorb it. The convergence ends, so the elves return to hibernation defeated but secretly relieved that Frigga is going home and hoping that they won’t meet any more like her at the next convergence.
Tldr: The Dark World ‘nobody dies–everybody lives’ remix
Or, an apology for letting Frigga die in a recent chapter of my fic.