I like to believe that babies choose their families. So if they ever have another child, it was that child that they lost (or chose to lose). But if they don't, it's not really an angel baby. They lost the rights to it.
Not unless it was aborted due to serious medical reasons. If it was aborted because it wasn't wanted, then it's offensive to call it an angel baby. You didn't want it, so why call it something like that?