Very interesting post. I think there is a significant flaw in the premise though as it doesn’t consider the element of time. In cosmic terms, humanity has barely been in existence, and will become extinct.
Time and existence is forever though. There is near certainty of life on other planets, but it doesn’t mean they will exist at the same time as we do, or in any proximity near enough for any of us to recognize the others presence.
I don’t think this would impact religious beliefs even if it did occur, as the same could be said about evolution or carbon dating. Faith finds a way to persist due to culture, norms and uncertainty regarding the unexplainable.