Allah Is Dependant
I think the question assumes that Allah’s plan was uncertain, but that’s not the case. Since He is All-Knowing, He already knew exactly what Adam and Eve would do. The idea that one could kill the other and end humanity was never a real possibility. Allah isn’t dependent on human action..if needed, He could have continued creation in another way. The test of life is about free will and accountability, not about reaching a certain number of people. His wisdom and justice are absolute and nothing happens outside His perfect plan.
This is God choice. And He first take the consent as we have told in another post.