In order for extraterestrial life to have fallen, they would have to have disobeyed a command from God, such as don’t eat from the tree.
To be of God’s children, they would have to have been willing to sacrafice something/someone of high value, like Abraham was about to do. And God would have had to accept them as His children.
To be of God’s adopted children, they would have to be baptised and accept Jesus. And have the Faith that this is good enough for God.
Extraterestrial aliens, if they exist, would have the same status as dogs. Or monkeys. As the intelligence of any creature pales in comparison to God, the intelligence of ET is NOT a condition for entry into heaven.
I would not make the lack of certain piece of scientific evidence a condition of proof. Future technology may be able to overcome this barrier. The Catholic church made that mistake with Galileo.
The evidence is a necessary condition for the existence of these extraterrestrials. The Catholic church DISREGARDED the evidence. I am honoring the evidence. Big difference.
If they exist, they leave a trace. If no trace may be discovered, they do not exist. Valid logical argument.
Our current technology is sufficient to detect the synthetic signal if it existed. It is not due to want of technology.