With humans everything is always 'could'. Which is just another way of saying that apart from death and taxes nothing is certain. As for cultural decline? Every generation regards those that follow it as having less 'moral character' previous generations. Yet somehow civilization has managed to survive the baton being passed on to new hands (mostly). As I've said before we'll see in due course. While humanity has proven itself (collectively) to be both capable and adaptable we are also appallingly bad at predicting the future.
Considering the Earth is just a ball on the cosmic billiard table it likely won't be ET's coming in from space that takes us (AND a whole lot more) out of the picture.
I don't think that's true. It's pretty clear that some generations have been better than previous iteration. Besides, that perception of decline is more often associated with - as you say - some kind of moral standard. But that's not what I mean by social/cultural decline. What I'm talking about is the decay of the social structures which support adaptability etc. IOW stable families and stable communities. Without that foundation, adaptability becomes close to impossible. Agility and resilience is lost, because it has no 'springboard' to keep powering it.
I believe we're very rapidly losing our adaptability, in the First World. Ingenuity won't account for much when The People refuse to adapt to it.
The only thing worse than discovering ET is finding the earlier texts of either the E author or the J author (or both). One either of those texts are found, it's over for Judaism and x-tianity, and by extension, Islam. That is an economics fail, a scientific fail, a medical fail, and a data fail. There is no data to support your claim. Scientifically, it is a virus and does not negatively impact any one group over any other group. Medically, those who have more than one underlying medical condition are negatively impacted, but please show us where 3rd/4th States suffer from rampant morbid obesity. Economically speaking, if you "thin the 3rd/4th World" then all 1st World economies suffer and go into decades long depressions, with a decrease in Standard of Living and Life-Style below that of the 2nd World. Yeah, that's right, you desperately need their labor and the Zero/1st Level Economic items they produce.