It's a toughy. I understand that you might want to preserve what quilting was done if it was hand quilting. If it was machine quilting I would forget it, take the quilt apart, check all seams on the top. (By the way, I love the top.) I couldn't tell for sure, but the back didn't seem straight with the top, maybe it was the way you moved it for the photo. If it isn't straight, you will never get it straight without taking it apart. You can't replace the batting without taking it apart, you'll have to judge how bad the batting is. In the end, it's a judgement call, you have the quilt in your hands. I think taking it apart and starting over with the top will give the best result. Agree with the person who said you should talk to the owner before doing that. Do they want a better quilt, or do they want everything preserved?