Alma 12:26

And now behold, if it were possible that our first parents could have went forth and partaken of the tree of life, they would have been forever miserable, having no preparatory state; and thus the plan of redemption would have been frustrated, and the word of God would have been void, taking none effect.

If Adam and Eve could have gone forward and eaten from the tree of life, they would have been sad forever. They would have had no time to get ready. The plan to save people would have been ruined. God’s word would have meant nothing.

If our first parents had been able to go back and eat from the tree of life, they would have been miserable forever, with no chance to prepare themselves. The plan of redemption would have been ruined, and God’s word would have meant nothing.