I have been lurking here and I really appreciate the posts. This child has only known one family, and it appears she loves them very much. The biggest gift her biological father could give her would be to let go. If he truly loved her and cared about her, he would Put his daughter's needs above his own. Isn't that what we as parents do? JMO
You can take a look at Michelle Knight who was kidnapped by Ariel Castro. During this time her son was adopted. Wasn't her fault that she couldn't see her son (since she was kidnapped and kept captive). She decided to not appeal the adoption as it's not in her son's best interests.