"Fell line" is a phrase that describes the fate of a character in a story or play. If you are in search of synonyms for this phrase, then you might try "demise," "downfall," or "end." Another option could be "tragic ending," "death," or "final chapter." Additionally, you could use "crash and burn," "ultimate fate," or simply "conclusion." Whatever synonym you choose, make sure that it accurately represents the idea of a character's fate in a story. It should convey a sense of finality, tragedy, and inevitability.