The whole question is irrelevant to sharing the gospel with a lost and dying mankind. It is useless in that it is spending time debating over hypothetical scenarios.
There is nothing in Scripture that addresses that issue and anything said on the subject is mere speculation and the opinion of man.
The issue of whether Jesus' death in regards to the earth and the spiritual realm is settled. Whether there is life on other planets is totally speculative at this point and and is likely to remain so for a LONG time. Unless some rational being breaks through to let us know that they exist, then the capability to detect and contact life on other planets is so far beyond our capabilities at this point, that it's meaningless.
As far as rational animals, which is not what the article that the thread is about is addressing, we have found none on this planet, save mankind and I'm not even so sure about that sometimes.
There are people dying and going to hell under our very noses every day. Our responsibility before God is to preach the Gospel and make disciples. Our mission field is our planet.
It seems to me that caww's understanding of the work of Christ is that it is local. It seems, on the other hand, quite clear to me that Paul says that it covers all of creation.
Now that difference of opinion goes to how one reads Scripture (which is certainly 'here and now' enough that a lot of non-Catholics have said we Catholics don't do it properly) AND how great a miracle was wrought through Christ.
You talk about sharing the Gospel with a lost and dying humanity. Certainly in one sense it is enough to say, "Jesus Christ, God the Son of God, the all-powerful, loves you enough to save you and is well able to save you."
But as I think of Psalm 18, with its wonderful description of God straining the seams of Creation [Hailstones and coals of fire!] to come to the aid of the Psalmist, I can't think that the question of whether the redemption wrought by Christ was local or universal is unimportant.
And I think Paul provides the answer, so I am not leaving Scripture behind as I think about the question.