Oh, God, that's a disturbing thought to me. But then, it all is! I don't think Bertrand has the temperament for parenthood like he would like to think. Mourning Alec, he'd look for him in Isabelle, and failing to find him there would leave him frustrated with and distant from her. There would be a hot and cold of him pushing her away and making attempts to bond and recover something of the bond he and Alec used to have, and eventual sexual abuse in her teens, but not as comprehensive grooming as Alec inflicted on her. Importantly, Bertrand also wouldn't discourage Isabelle's independence the way Alec did, and sometime in her late teens or early twenties she'd be unleashed as a "deeply dysfunctional but still able to get by" adult.