Gee sorry to here the troubles on this quilt....there is a lot of reasons why the tread can do what it is doing...10 years is a good long time...if it has been washed a lot ....type of thread...like poylester and tempurture of the water was to hot... or harse soap....if the sun shined on it....etc....
My Dad requilted a quilt....mainly he just sewed it together so it would not fall apart and it was useable....he did pick out all the old stitching... it came out nice
How is the applique put on...hand stiched??? do you feel it needs new batting???? I think there is alot of different things you can do....since it is so important to you ...what you have in mind would make it last longer...good luck....