He will chew a hole in it!
A fix was in order. I didn't take photos of all the steps, but here they are...
1. Slip a small square of muslin between the muslin backing and the batting. Pin in place from the back.
2. Flip over. Re-position batting in the hole. Pin a larger piece of black bridal netting to the front to keep the loose batting from being caught in the feed dogs. Flip again so backing is facing up.
3. Using darning or free motion quilting setting, machine stitch around the hole. Mend the hole (from the back) with vertical and horizontal rows of straight stitching.
4. Flip over to the front side. Trim away excess netting.
5. Cut a heart applique to cover the hole and repair stitching from the front. I used a bit of Heat N Bond to hold it in place.
6. Zig-zag applique the heart to the front of the quilt. I used 2.5 width and .5 length.