That said, the fact that your lender may be going bankrupt should not affect you at all. Your loan would likely be sold off or assumed by another lender subject to the terms and conditions you agreed to when you signed it—terms that will not change. You have a legally binding contract that not only obligates you but also protects you.
I caution you to watch your mail closely and be wary—even suspicious—of anything you receive regarding this matter that does not come from your current lender. It will send you a directive about where to send your payments in the future and who will be servicing your mortgage. These days there are crooks who prey on the vulnerable and take advantage of people who are facing unfamiliar yet public situations. I predict that at the very worst you will receive a letter instructing you to send your payments to a new address.
Should you receive anything more than that, make sure you speak with an attorney or real estate professional you trust.
I suppose that in the worst case ever, you could sue for the ring to be returned to his estate. But I cannot even imagine it coming to that—let alone a judge finding for the plaintiff.
This woman’s possession of the ring and the circumstances would more than likely convey ownership to her. She could sell the ring or give it away, both of which would indicate ownership. Taking this to small claims court would be one for reality TV, perhaps.
My advice is to see this as a gift your father gave to his intended and a relationship that brought him great happiness, not one that could have ever replaced your mother. That he died before they could be wed must have been heartbreaking for all of you—including his fiancée.