Oh, the times I use a sentimental quilt as filling is only for that original person! Mostly I see it as children growing out of their blanky, they don't feel the same way when they grow out of their twin quilt. Sometimes it is a queen size quilt and sometimes reusing that original quilt is a way to move into the future while keeping a quiet piece of the past. It's usually a special personal request and it isn't usually a top I originally made.
In the case of my husband's quilt, that was just practical and that back is going to last a lot longer than the front and so maybe it will end up with yet another layer in time.
Now I have been known to use a wool blanket I've gotten at a thrift store as a batting for a new project but I'd say that is different.
Edit: Mim, I should have said I'm sorry for the circumstances that have led you to this question. If all hope is gone for them, then I think a burning ceremony is the way to go. Some projects I can let go to the dog beds and eventually trash but some would hurt more to see them treated that way.