I remember Alex once told me: Adam was incorruptible prefall while Jesus was corruptible in incarnation. I agree with the latter, but the former is questionable. Perhaps Alex was just trying to make it of an literary art.
But the question remains: Was Adam truly immortal when he was created? After some research, especially with the new upgraded Logos 10 Gold Software, full feature without any library addition, I was able to easily look for some reformed answer to this.
Basically, the answer is, Adam was not likely immortal. As far as the reformers are concern. The Baptists, fundamentalists may have the immortal view (i.e. John Gill's "Adam, upon sinning, was at once stripped of the immortality of his body..." ~ A Complete Body of Doctrinal and Practical Divinity Vol1. p 461) or "provisionally immortal" by Methodists like Adam Clarke (The Holy Bible with a Commentary and Critical Notes, Vols. 1-VI, Ge 5:12; V1, p 64). But because his mortality is unknown in prefall and that had he not sinned, his incorruptibility would be guaranteed, therefore in this sense, we can call Adam immortal or incorruptible before the fall, as that was the goal of it all.
Most reformers viewed the tree of life not an actual giver of immortality. Lane Tipton was aware of this as well in his TH221 Doctrine of Man. It is a sacrament, a seal, confirmation of immortality had Adam obeyed righteously. Tipton also said in the work/video (which I don't have), that Adam "Why does Paul speak this way? referring to 2 Corinthians 5:12, I believe,,,Adam, while created very good and sinless, was not created in a glorified eschatological state...was not clothed in the full perfection of righteousness and holiness. He was not confirmed in glory and immortality. Adam's pre-fall body exists in the estate of innocency, not glory."
For John Calvin, what's withdrawn was the assurance of it, it was not immortality that was removed. It's also interesting to note that in his Institutes, Calvin stated that even if Adam had eaten from the tree of life after his sin, he would not have had immortality restored. Those Genesis verse God was speaking in was referring to Adam's vain confidence in the tree of life, not a true cure.
John Calvin's Institutes Book IV. Chapter 14.12:...when he sees meet to withdraw our assurance of the things which he had promised in the sacraments, takes away the sacraments themselves. When he deprives Adam of the gift of immortality, and expels him from the garden, “lest he put forth his hand and take also of the tree of life, and live for ever” (Gen. 3:22). What is this we hear? Could that fruit have restored Adam to the immortality from which he had already fallen? By no means. It is just as if he had said, Lest he indulge in vain confidence, if allowed to retain the symbol of my promise, let that be withdrawn which might give him some hope of immortality...
...14.18: Calvin also used the Tree of life to Adam and the Bow to Noah as sacraments. In that, the rainbow itself does not confine water, nor the tree of life actually give immortality.
Charles Hodge's view is that the Church Fathers embraced a sort of probation period for Adam's mortality-immortality uncertainty.
Charles Hodge's Systematic Theology Volume 2, Page 116, Chapter V Original State of Man, #6 Pelagian and Rationalistic Doctrine...With regard to this subject it is to be remarked that there are two distinct points to be considered. First, whether Adam would have died had he not sinned; and second, whether his body as originally formed was adapted to an immortal state of existence. As to the former there can be no doubt...The second point is much less clear, and less important...one view...Adam was to pass his probation...translated to the heavenly paradise...Luther...tree of life...to eat had they not sinned...to preserve their bodies in perpetual youth...others...had he maintained his integrity, would have undergone a change analogous to...those who shall be alive at the second coming of Christ...the corruptible shall put on incorruption, and the mortal shall put on immortality...then his [Adam] body...required to be changed to fit it for immortality.
Martin Luther in his Genesis 2:17 commentary stated that Adam could fall and because of that, this given immortality, sustained by the power of the trees for him as food, has not been made sure and it is not our business to investigate why God created man in this "middle condition", contrasting the creation of angels.
Martin Luther, Luther’s Works, Vol. 1: Lectures on Genesis: Chapters 1-5, ed. Jaroslav Jan Pelikan, Hilton C. Oswald, and Helmut T. Lehmann, vol. 1 (Saint Louis: Concordia Publishing House, 1999), 111–112...Adam was immortal because the trees created for him had the power to maintain his life unimpaired. But this immortality had not been made so sure for him that it was impossible for him to fall into mortality. It is not our business to determine or to investigate too inquisitively why God wanted to create man in this middle condition, or why man was so created that all people are brought into being from one through procreation. The angels were not created in this condition...
Geerhardus Vos consider Adam's state of immortality not apparent or awaiting in the covenant of works.
Geerhardus Vos' Reformed Dogmatics V2,
p 16 (p 196 in my digital copy): #19. What must be said concerning the question whether Adam was mortal or immortal? Vos compared 5 different kinds of immortality.
p41: #16. How can one show that there was a specific promise in the covenant of works?
...c) The same follows from the parallel between what Adam should have done and what Christ has done. The latter has brought eternal life and immortality to light (2 Tim 1:10). Adam, too, would have done this if he had not succumbed in his probation.
Herman Bavinck treated it carefully, so it may seem at first he supported the immortality view, but when read further, it's not as simple as one may think. In fact, he even called immortality not natural.
Herman Bavinck's Reformed Dogmatics, Volume 2: God and Creation, p. 560. Part V: The Image of God #12 Human Nature:
...Immortality and impassibility could not strictly be called natural...belongs to the essence of man and to the image of God, it originally also participated in immortality. God is not a God of the dead, but of the living (Matt. 22:32). Death is a consequence of sin (Gen. 2:7; 3:19; Rom. 5:12; 6:23; 1 Cor. 15:21, 56). In the case of Adam, however, this immortality did not consist in a state of not being able to die (non posse mori), or in eternal and imperishable life, but only in the condition of being able not to die (posse non mori), [from Augustine's conception of freedom] the condition of not going to die in case of obedience. This state was not absolute but conditional...
On an interesting side note, in the same paragraph: "The incarnation of God is proof that human beings and not angels are created in the image of God, and that the human body is an essential component of that image...God could not have been able to become man if he had not first made man in his own image."
Bavinck also stated in his Reformed Ethics, available in two volumes digitally but I have yet to obtained at the moment, Reformed Ethics, Volume One, p. 252..."Physical life cannot be immortal of itself, not even in Adam, in whom it might have been eternalized through the spiritual."