The consistent story is that Disney will turn you away if there are no new reservations available. It’s unimaginable, but seemingly true, that the system cannot convert your current reservation. According to CMs, your cancelled reservations do not become available to you. I don’t know how the system really functions.
The other option is the Hotel Bucket of reservations for people staying onsite. If you book a night at Paradise Pier, as of now, there’s reservations for all of your days.
There are also posts on this board that indicate that you can book a stay in the future and make current park reservations. I have no experience with this so YMMV.