Except that doesn't invalidate anything at all. Mankind, the one truly made in his image, fell. And God came and is now in the form of man, not some alien flesh. A man now sits on the throne of heaven. A proper trinitarian and incarnational understanding of God and creation is required, of course, but since most Christians are functional gnostics, they might be confused on the point.

But just because one race fell doesn't mean every other hypothetical race on other hypothetical planets also fell or also carry the special imago dei.

The Fall was tragic, but God did something even more wonderful than He would have before. He could have glorified other races in lesser ways.

Again, Lewis speaks of this.