I don’t know how either of these possibilities will ever worm their way into existence short of the apocalypse descending upon us, since, after all, the physical end of human history as we know it would constitute a complete absence of the future. But then, SF wouldn’t exist because there would be nobody there to think about it. So that is not a possible solution to the problematic nature of SF’s mortality.
Instead, and I think I have touched on this at some previous point, science fiction will cease to exist in the first instance when some measure of hope (or the utopian ideal of such a thing) no longer occupies us as a bulk entity of fleshy masses, when we literally cease concerning ourselves with the present’s pursuit of the future. How? Perhaps through the creation of a utopian state, as much as one can exist, in which the needs of each man and woman are attended to, in some fashion or another. It’s hard to say what could produce the incapability of imagining the future, but when that occurs, SF dies.
In the second instance, however, the future must cease to exist because the limitations of the future itself are as mortal as science fiction. The future is not indefinite, but is replaceable, recycling itself over and over, in a cycle that is finite. It is not a perpetual motion machine, but a machine with a long, slow, drawn out cease-ment-of-living. The future, thus, ends for mankind when there is nowhere else to go. Perhaps that is at the end of life as we know it, or at the end of the universe (the collapsing of the energy that created us all, which would then restart the cycle, restart time like a battery). More than likely, it is at the point in humanity’s inevitably long existence in which we simply have nowhere else to go. Imagine that, if you will: after all those centuries, we come to a point where technology cannot progress, where what is around the corner is little more than the same thing that we saw yesterday, and nothing we do changes anything in a significant manner whatsoever (on a global or galactic scale). That is where science fiction dies.
But, a simpler approach, one that is less “philosophical,” if you will, is to try to think about the place we will eventually be in, where science fiction cannot possibly offer us anything else. If we already have space ships and aliens and AI and robots and all of those imaginative constructs, then, really, where else is there to go? Science fiction simply cannot exist in that sort of environment. It will cease to be speculative and forever become the present, the every-day. We'll stop calling it "science fiction" and, instead, shove it in with all those mainstream and "literary" novels. That is, of course, if literature can survive the distant future.
And that’s all I have to say on that. What do you think?