At our recent conference, I suggested that if Adam and Eve had not eaten the forbidden fruit after a reasonable period of time (e.g., three months), God would have removed the temptation, and He would have changed Adam and Eve so that they and their descendants would thereafter be unable to sin. One online viewer of the conference sent in this question: “Where do we get the idea that God would have removed the tree of the knowledge of good and evil?”
There is no specific verse that says that. But I believe it is a reasonable inference based on other teachings in Scripture.
First, Lucifer and one third of the angels fell (Rev 12:4). There is no indication in Scripture of any subsequent fall of any of the angels that did not fall. Surely if there had been another fall, God would have told us. That suggests that God sealed the unfallen angels so that they could not fall in the future. If God did that for the angels who did not fall, He would have done that for our first parents if they had not fallen after a reasonable length of time.
Second, every believer in Jesus Christ will be incapable of sinning once he goes to be with the Lord. If we die, we leave our fleshly desires behind. When the Rapture occurs, all church age believers will be glorified. We will be incapable of sinning forever. If God will do that for us, He would have done that for Adam and Eve after some time period. We might argue whether God would have sealed them in innocence after months or years. But at some point, it surely would have happened.
On the new earth (Revelation 21-22), there will be no sin at all (Rev 21:27; 22:15). All the humans there will be fully human, yet without sin.
It is wrong to think that one must have the ability to sin in order to be truly human. God’s original desire was for a sinless humanity. That desire will be achieved on the new earth in the eternal kingdom.
Since what is finally done in Revelation is the completion of what God began in Genesis, we can reasonably conclude that God would have removed the ability of our first parents to sin after some time of testing.