That's heartbreaking. It sounds like it wasn't intentional with the dog, but very frustrating to see what happened to your hard work, which I'm sure you put a lot of thought into as well as time and expense. I'd only offer to repair it if you think they WANT it repaired. Did they show regret/remorse for what happened to they quilt? Are they heartsick? If so, you can be generous and give the quilt more time and energy with repairs. If not, you might want to leave it be and just resolve to not make any more big quilted projects as their gifts...perhaps a small utility lap quilt, a table runner or something that won't take as much effort or be quite so frustrating to witness if they don't take care of it.