I have theory:
There is minute indications that a number of civilization have had reached technological superiority in one way or another long ago but they all vanish. I believe the human race won't end but there will be something that will destroy a large number of humans. once, the populations is decreased drastically, we'll loose all the knowledge we have gained (specially the one we gained in last 200
years).
Now, how would a large number of humans die, well, it can be earth quacks, floods, typhoons, ice age etc etc. But what I believe is that by the rate earth is getting warmer and warmer, the polar ice will melt and the viruses, bacterias etc all that stuff that is frozen for millenniums will come to life and one of those viruses will kill a lot of humans.
what you say? a little too much?