I am so, so sorry to read this. Kicking up a fuss with the post master and the local news station are good ideas to follow through on.
My DH laughs at the amount of tape I put on boxes: across the centers, X-ed across the centers, all the way around the box in at least four places, across any place where the box isn't attached to itself.
We send everything Priority Mail, weigh, and print the label at home. So more tape across the box, the return address part of the label, and back across the box on the other side. Repeat with the Name and Address part of the label. The only part you need to be sure not to put tape across is the bar code (the machines can't read through the tape).
Label "fall off"? I don't think so!
Oh! And I never write "Fragile" or list the contents of the box (if I have to, I put "Return of linens").
Roberta, I pray that somehow they find your quilt ..... maybe after a photo of it is seen on TV .....
Fear of loss is the main reason I still haven't sent PINKS & Fairies, the log cabin for my DGD, to the longarmer.