Thanks for your post. The whole Gospel story is ruined, that is why. God does all things for His glory. The bottom line on this is that the enemy of our souls cannot create.
But, he does dilute. So whatever God does, the enemy dilutes and confuses. Thus we have many world ‘religions’ because it confuses the mind and heart of man to have the alternatives. Most of them are mostly true.
God created for a purpose - to give Himself glory. If we see ‘aliens’ it is my considered opinion that the aliens will claim to have placed man here, thus diluting and confusing the creation claim of God.
The Bible tells us that there are two types of eternal and sentient created beings: angels, and men. Among the angels, some are fallen, and for them there is no plan of redemption. Among men, all are fallen, but there is a plan of redemption.
Thus, living creatures, if sentient, must be either angels or men. (A third possibility would be that sentient beings exist that are not eternal, and thus, the question would be answered in that way.)
These beings are clearly not men or they would be recognized. But the Bible says that the enemy can appear to us even as an angel of light. Since the Word attributes to our enemy the ability to change his appearance for his own purposes of deception, it stands to reason that he can appear as an alien.
Thus, aliens, in my opinion, are fallen angels, deceptively appearing to take credit for what God has done. There is no plan of salvation for them.
There is NOTHING in the Bible that contradicts the possibility that God might have created other sentient beings in His image at other places in His Cosmos. By your definition, they would thus be "men". Since God Himself is not a material being, whatever aspect of man that is "in His image", is obviously NOT our physical form. We simply do not know exactly what that applies to.
This concept takes NOTHING away from the Gospel, which applies to OUR situation here in THIS tiny portion of God's creation. For all we know, the other "men" never failed God's test, as Adam did, and are currently living in the same union with the Creator that Adam lost.