We have no idea of knowing what a sapient specie's likelihood to die out is, since we're the only known example. Reaching some kind of technological event horizon seems like a very optimistic view of the direction of human civilizations.
This current exponential growth in technology dates to the industrial revolution, and depends on a pretty fragile balance. There have rarely been continued periods of technological progress without huge upsets and loss of knowledge. Added to the natural catastrophes that could lead to such a thing is a heightened danger of human-made disasters. Probability wise I think you guys are giving way too much weight, even certainty, to this "post-human" thing.
The nestled (think russian matryoshka dolls) realities/dimensions/simulations has been explored pretty thoroughly in mysticism, religions, philosophy and science fiction, but so has the idea of an apocalypse and general downfall of civilizations or complete/partial extermination of humankind. They're more reflections of our psyche than prophecies imo, at most they are possible self-fulfilling prophecies.