I hear you but most people say that just to get out of a situation easily. The reason why the mother didn’t want it will never change. In a case like that I don’t think there is hope. In a general case where they are just not interested, then what you said before could might make sense but still don’t think it’s right because that’s giving them false hopes. In this case, it doesn’t seem like it’ll ever happen again.
Sometimes a lie is allowed and I wouldn’t really call it a lie anyways. If you told him the truth it might make him worse and that could probably lead him to go off the derech. So, in this case, you could possibly be saving his life by not telling him the truth.