Well, we know that by the 'Manhattan' episode, Rumple and Emma are off on their quest so the scene cannot be postponed for too long. I reckon Gold not only asked for a favor but also blackmailed them – he's the one who knows most about magic and Cora so he is crucial in protecting SB, especially that Regina's stand is uncertain. He could've offered another deal – if Emma doesn't come with him, he will leave anyway and for good, find his son and not ever come back. However, if Emma does agree to come, she will make sure they find his son as soon as possible and then they will ALL come back to SB to deal with the problems.
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