That is certainly not impossible but the situation is almost a formula divorce- husband abducts and kills scenario. Badgering hell out of a woman who is probably emotionally full of cracks already because of her missing child, regardless of whether she is the agent of the disapppearance or not, seems calculated to reach such a result as did, in fact, occur. Killing off thelady certainly does not bring solution to the mystery any closer and may make it more difficlt or impossible.
Maybe she does--we would have been better off if she were alive and able to tell us he is, though, wouldn't we?