This exact situation is why my husband and I were unwilling to even consider a domestic adoption, and why we adopted internationally. With international adoption, there is no chance the birth parent will come looking for the child and demand a do-over take back, and there is no chance for the birth parent to be a disruptive presence in their life as they grow up.
I have known 2 situations where the birth mother re-claimed the infant, as well as personally knowing several situations where a very disruptive birth mother created ongoing havoc and chaos in "open adoptions."
Personally, I don't believe that most of the American adoption laws have the best interests of the child in mind. They are crafted to give birth moms (who don't want to be parents, and typically have a ton of social problems) what they want on their terms-- ongoing access to the child, but relieving them of actually parenting the child. There is no regard for the child's mental and emotional well-being in open adoption policies, IMO. And "take back" laws beyond a few days are never in the best interest of the child, IMO. The birth mom needs to make a decision and stick with it, for the best interest of the child, IMO. Raise the child themselves, or make an adoption plan and stick with it.
I also strongly believe that "open adoptions" are almost never a good situation for the child's well being. I know they work for some people, but as a general policy from social workers, I think it's a disaster for the child. I believe the child should have a chance to grow up in a secure and non-chaotic situation, free from the imposed additional situation of the birth parent. Once they're 18, if the child wants to know the bio parent, and the bio parent wants to know them, then let them meet. The adopted child deserves those 18 years of their ONLY childhood to grow up and form an identity apart from the bio parent, IMO. I grew up with one of those chaotic birth parents periodically showing up and inducing emotional havoc, so the issue is near and dear to me.
I know there are isolated circumstances where open adoption seems to work, but I personally think kids should not be burdened with the "needs" of the birth parent to be in their lives while they are growing up. Open adoption is all about the wants and desires of the birth mom to have it "both ways"-- let someone else do the hard work of parenting, and show up as the "birth mom" when it's convenient. As a social policy, I think open adoption is pretty wrongheaded.
At our pre-adoption classes, we had to sit thru a panel discussion, and other episodes where bio moms in open adoption situation talked to us about their circumstances choosing the couple to adopt their baby. I could not believe that 2 of these bio- moms actually talked to us about circumventing adoption agency policies to create little "tests" for the parents who eventually adopted their child. If the prospective parents wouldn't play their little games, the bio mom crossed them off the list.
My husband and I know full well that there probably isn't a pregnant teenager on the planet who would consider us "cool" enough to adopt their baby, so we never seriously considered domestic infant open adoption.
My heart aches for this poor baby who was killed, and for the couple who loved him. That child was much better off with the loving couple, than with 2 immature young teenagers. Just because someone can breed, doesn't make them a good parent. That baby was not better off with his 16 year old mother. Yes, that's very opinionated, but that's how I feel.