Should you be held legally and morally accountable for someone's death if you had the opportunity to prevent it?

Scenario

Suppose you saw a complete stranger walking on a rocky terrain. He is too indulged with their phone as they continue to text without being aware of their surrounds. You notice they are starting to walk towards a cliff edge leading to a 200-foot drop, but you can take a simple action to prevent it at a low risk or little cost to yourself.

Is it immoral to do nothing in such circumstances? Should just standing idly rather than taking steps to save a life be a criminal offence as you have potentially just let another human die?

Legality and Morality

If an individual detects an act that seems, from their perspective to be an injustice such as watching an attack play out or something that may very soon lead to a perceived predictable injustice and that they could intervene to prevent or significantly mitigate the crime or the immediate consequences of such then I believe that anyone should take action or suffer the consequence of be held morally culpable only to themselves and only by themselves.

Regarding the legal accountability, I think as individuals, we are not legally responsible for the health and safety of all members of our society. Our laws reflect the consensus moral viewpoint of our society. However, some laws are disputed which people don't believe in or support. Although we may not be legally responsible, is letting a life perish as bad as someone who commits a murder?

A person who is wandering off a cliff due to their own distraction is being negligent to their own safety. So we now have a conflict - am I responsible for your own lack of responsibility? Am I to be held negligent for not stopping your own negligence?

Even if the risk to myself is minimal, must I be expected to risk myself at all to stop your own negligence from hurting you? If we are going to hold people to a standard high enough that they should be responsible for the safety of strangers - should we not at least hold them responsible for the safety of themselves first?

In the end, I would say that while helping a stranger in that situation is a moral virtue, it should probably not be a moral obligation but if a circumstance like this ever happened to me I, of course, would try, with the best of my abilities, to help and warm them.

However, this argument bears more weight in you being in the wrong if you do believe in 'God' as the inactive omniscient observer of injustice.

Conclusively I think that it is morally good to act. However, not acting, while a bad action, should not win moral blame.