I did this not long ago. Fortunately still had the original fabrics left over! I unquilted the area then I re-made the chewed blocks. I then unstitched the chewed blocks from the top. Managed to re-sew the new blocks into the top...probably by hand - sorry, don't remember exactly. I then hand patched a piece of batting and then ultimately 'appliqued' a piece of the backing over the offending hole. Re-hand quilted the area. It really wasn't as horrible as it sounds. The original hole was large enough for a large hand to fit through with room left over. The backing was a Moda marble flannel and hid the repair very nicely. By the time all was completed, you could not find where the original hole had been except for a slight color difference from the original fabrics due to wear/washing.