I recently saw an article on the Creation website that set out to answer the question as to why God 'imposed' the death penalty on Adam for his sin.
As one could expect from a fairly theologically traditional organisation (I generally agree with their theological position in its dependence on the Bible, but I find that some traditionalists have allowed, I think, cultural influences to bend their theology; perhaps this is exemplified by such things as culturally traditional views of relationships with women, church order, and an overly forensic approach to theology).
The way Russell Grigg puts it in his article, it sounds as if the 'death penalty' is imposed in a discretionary manner because a law had been broken. But not so. The law was not given until many centuries after the fall. So, what happened?
God made Adam in his image, to be in a way a counterpart to God such that real relationship could be between the two: creator and creature. For real relationships, the imageness would need to include a real will, real capability for decision making to form a real relationship, and not just to mimic a relationship. God was, to adopt our language, taking a risk. But I'm sure he knew the possible outcomes and had them all 'managed' (as we like to say that we do with risk these days!).
The tree was presented to man as God setting the footing of the relationship: it was a genuine relationship, not an orchestrated one. Man could remain in a relationship of life, or turn from the relationship and cease to participate with God; that is, man would reject the one who had in himself 'life-source' as the foundation for the work of 'subduing' the creation (living within and caring for it, and not dominated by it). He would here live in life, but rejecting God, he would now live in rejection of the life-giver and so, in the struture of it would inherit death, purely on his own choice.
The 'death penalty' arrived because Adam choose to separate from life and 'know' in his own life-experience the evil of choosing 'not-life'.