What a strange thing that's happened to your binding. If you have more of the same fabric, I would take out the ripped piece & splice in a good piece & finish the quilt. If you don't have enough of the same fabric maybe you could rip out each corner of binding & splice in a piece of different fabric on each corner making it look like it was suppose to be made that way. No one will ever know if you don't tell them.
Hope this makes sense.