I find it really interesting that Erik's fantasy seems to be Christine promising to do anything, possibly including dumping Raoul, running away with him ect. ect. whereas Jareth's fantasy is just Sarah needing his help, not her promising him anything just her reaching out to him, her needing him, her wanting him. All he wants is the chance to safe her, for HIM to be the one she reaches out to. He wants her to want him, not to be bound to him. I find that her asking for help is enough to shut down his brain due to fantasy fulfillment both very beautiful, and very sad.
....orrrrr the implicit power trip for him, the bargaining opportunity of Sarah being in dire need. Or just StraightArt!Sarah in bondage.
Not to take a dump on your being moved by the moment or anything. But no, disregard my flippancy: it's kinda true. Jareth does desperately desire cues from Sarah that give him another role to play than her antagonist, a sign that she is willing to see him in another light. Not that his second instinct wouldn't be to use the situation to his advantage and make it a power play, but yeah, there is a heartbeat's worth of something else.
Oh, I have no doubt that he would do everything in his power to turn the situation to his advantage, of he had retained the powers of speech, (not that I can blame him StraightArt!Sarah indeed) but it was the heart beat of something else, the fact that deep down he really doesn't want to be her villain that got to me. You see more of it later but here's one of the first hints in comic that he really wants something else. And, even if he would have messed it up in the second flat if she had asked him to rescue him (as demonstrated by KIDNAPPING HER FRIEND AND ROOM MATE AND MAKING THE WHOLE THING WORSE (face palm)) it's his to see that part of him.