OP - EC 261/2004 would entitle you to cancel your ticket for a full refund. You may then purchase whatever else you want or not, as you choose. But the Regulation does not require AF to cancel specific segments and refund those. Additionally, as others point out, even if AF did so, it is entirely possible that FDF-ORY as a single costs more than your current open jaw and thus you would see a net add/collect due by you to AF and you would still need to get yourself to MIA or FDF as the case may be.
It would be helpful to understand what you are trying to accomplish here, what flexibility you have, and how you are traveling MIA-FDF.