Other, better, smarter people than I are writing about the impact COVID-19 will have on economies, lifestyles, most everything really. Here, I'm going to jot down a few notes coalesced from some things I've been thinking about science fiction and fantasy — the former more than the latter.
My original thought went like this: SF has a shelf life that fantasy generally does not. But then I revised it to this: SF and fantasy both have shelf lives, but drastically different kinds, something exposed by paradigm-shifting events.
The obvious reason why hard SF ages out is because the real world passes it by. The harder the SF, the shorter the shelf life, unless there's something else going on with it. A good story that isn't welded end-to-end to the hard science in it has a better chance of surviving the ages.
A couple of examples come to mind. Harry Harrison's One Step From Earth, an anthology of stories revolving around the concept of the matter transmitter, has a central idea that may never age out. When are we ever going to invent teleportation? (If we did, that would change a whole lot, now, wouldn't it?) But much of what Harrison treats in the stories are analogues of how every new mode of transportation irreversibly changes the face of the society that develops it. And the other parts of the story that are at risk of aging out are buttressed by good, insightful storytelling. Even if we did ever invent teleportation, there would still be a lot to chew over here.
Case #2: John Brunner's proto-cyberpunk Stand On Zanzibar and The Shockwave Rider, despite being written in the 1970s, are still fresh and prescient; the latter foresaw not only the internet, but Wikileaks (minus its weaponization ... maybe Brunner was saving that for another book). What the tech is about is less important than what it means. Some of the cyberpunk from the 1980s has dated, but not all of it. The technology's passé, but the social attitudes ("the street finds its own uses for things") have become only more relevant and urgent.
When SF dates irreversibly, that's a sign it didn't have much going for it beyond the novelty of its moment. For an SF story to have legs, it needs to have more than just some clever conceit. What matters in such a story is not just what happens (people invent matter transmission) or how it happens (dimensional portals, essentially), but what it means to everyone involved (every aspect of human life is upended). Once the tech ages out, the story has to stand on its own, or else.
Fantasy, though, has a different shelf life. Hard SF is dated by changes in technology and scientific understanding. Fantasy is dated by changes in society and our understanding of human behavior — something that happens on a far deeper level, but more completely and thoroughly, and which can (and often is) fueled by changes in technology and scientific understanding. Actually, SF is dated by changes in society, etc., too, but fantasy is dated more directly by them, since more of the story revolves around them in fantasy.
Magic systems and such don't date, because they have no shelf life to begin with. Except maybe in the sense that a given trope becomes tired, and needs reinventing, or reveals itself in time to be sterile. For instance, I have never been a fan of the "magic system" subgenre of fantasy (Brandon Sanderson comes to mind), where the mechanics of the fantasy world function as a drop-in for the way technology operates in SF. We're now seeing the rise of a whole sub-subgenre of fantasy, "LitRPG", where the game-mechanic aspect of the storytelling is made explicit. At least they are honest about it. But I digress. All this for me is why Star Wars always classified as fantasy by the taxonomists: the mechanics of the Force (or even an X-Wing) weren't important in the way Darth Vader being divided against himself was important.
What ages fantasy out is when we realize we now know more about life than it does. The Lord Of The Rings is still worth reading, and still has a great deal to say, but it was the product of a less sophisticated (read: cynical) world than ours, and there's no working around that, even if Tolkien wrote it in the shadow of not one but two world wars. It has not aged out as such, but it is clearly the product of another time, one receding further with each year. At some point we might look back on it and shake our heads that we ever took it seriously, but that seems a long way off.
Lensman was more pulp fantasy than SF, although its vision and sweep haven't kept it from aging badly on many other fronts. It's the product of a retrograde view of men (and women, cough), and that makes it hard to take on anything but a superficial level — harder, in other words, to feel like it has anything to tell us about ourselves, even in a fantastic way.
A good fantasy dates very little across decades, because good insights about human behavior tend to remain timeless. That's the case with most any good art or fiction, even if we need to unpack its significance by way of scholarship. (Melville's reputation as a great of American literature only came decades after his death, thanks to those who kept his torch lit and held high.)
When most science fiction ages out, it's because its what-if has become a been-there-done-that. When most fantasy ages out, it's because its once-upon-a-time has become a good-riddance.