According to the CM I talked to (for what it's worth), if you were unable to keep the RO at the beginning of your reservation, you would still be able to use your Magic Bands during a stay a WL. He said all that would be required would be "a simple set up and tap at the front desk at WL"
I asked if it would affect any of the FP selections and he said that no, as long as your MYW package (with the room and tickets) is active, your fast pass selections will remain intact.
(This conversation was about if we booked and no-showed the reservation --which is what we were thinking of doing--I did not ask about canceling, but it seems like it would be the same either way)