Sweet! Looks like there's a lot of gilt still on it! I found one with nearly 100% of the gilt once, and another with no gilt.
You mentioned reattatching the back. Is there a hole in the back where the loop came off? If so, you may consider having someone try to remove the "push" from the front of the button while there is a hole in the back to insert a rod to push it back out. Then get the loop reinstalled (if restoring it is what you want to do).