Yes, of course… that too is entirely plausible. However, such a personality is the embodiment of Mara / the Devil and can never be trusted to reveal the entire truth or not to add new twists in the future.
If we ‘freeze frame’ the flow of Samsara into the actual moment that X, gun in hand is making the decision to kill/ not to kill the person in chains what do we find?
In the immediate moment, there are two possibilities - either X kills or X does not kill.
Branching out from these two main courses of action there arise infinite numbers of possible outcome paths, each dependent on a different set of underlying conditions. In this moment, no one can be aware of all the underlying conditions and plot all future outcomes, hence it is not possible with any certainty to predict the sequence of events as they will play out ( MN90 - “There is no ascetic or brahmin who knows all and sees all simultaneously: that is not possible”).
It is entirely possible to be rewarded in the immediate future even for wrong action. Having one’s family freed in exchange for killing someone is such a reward.
However, there is one thing that can be predicted, and that is the future destination at which X will arrive, having started out with either course of action. Breaking the precepts leads to eventual rebirth in a bad destination, which cannot be avoided on the excuse that ‘I did it for the sake of my family’ (MN97).
Why do we keep the precepts? We do not keep them because we are enlightened - but because we are unenlightened. Our minds are corrupted by the defilements, swayed by which we tend to make wrong decisions. The precepts act like roadblocks - they prevent us from choosing the wrong path.
In our present case, if X chooses to follow the precepts and not to kill, he chooses the upward path. The purpose of making an ethically correct choice is to have no regrets (AN10.1). If X were to come out of the situation alive, no one would find fault with him. Even if the Mafia were to kill him and his family in the immediate future, having kept the precepts, X is assured rebirth in a good destination (MN60).
If X chooses not to follow the precepts and kills the person, he chooses the downward path. Sure, the Mafia may spare X and his family and might even reward him … but that will not change the fact that having chosen to kill, X is now a Murderer. Possibly, a court of law would convict X - his action is blameworthy even though there are extenuating circumstances. Even if he goes unpunished by society, the effects of his wrong action will inevitably play out within him either in this life, or in the next. (For a commonplace illustration of this see the inordinately high rates of psychological illness, substance abuse and suicide in military veterans and police.)
How does this actually work? For a proper understanding we must examine the working of the Mind. X’s decision to kill / not kill is based on a large number of factors of which he is himself by and large unaware. The decision matrix includes the immediate information with which he is presented plus various other intangible factors based on previous social and cultural conditioning and the results he has previously obtained from similar actions. When X makes a decision to kill, his Mind’s decision matrix is immediately skewed in that direction. If he gets rewarded for that decision, he becomes even more likely to choose that course of action in future. Having chosen the wrong path once, he is more likely to go the wrong way again… and again… his Mind changes, acquiring unwholesome characteristics which inevitably result in his rebirth in a lower plane.
The precepts act as a large counterweight in the Mind’s decision matrix. This is why we strengthen them by reaffirming them at regular intervals. When sufficiently established in our Mind, the precepts prevent us from making wrong choices. This is why the Stream enterer - who always keeps the precepts unblemished and unbroken - is exempt from the bad destinations.