The Simulation Argument as advanced by Nick Bostrom suggests that we should give more thought as to whether we are simulated beings, running in a computer of some description. In essence, our present trajectory in technology suggests that there is nothing to prevent our descendants from running very detailed simulations of their past, including simulations of people - they will, after all, have access to staggering amounts of processing power, entire solar systems worth of matter converted into high grade nanoscale computing devices. Running a simulation of what is to them early civilized history would be a trivial expenditure given their vast resources, so they will probably do this many, many, many times. Therefore any random pick of what appears to be a human living in the natural universe is actually much more likely to be a simulated human living in a simulated environment:
This paper argues that at least one of the following propositions is true: (1) the human species is very likely to go extinct before reaching a "posthuman" stage; (2) any posthuman civilization is extremely unlikely to run a significant number of simulations of their evolutionary history (or variations thereof); (3) we are almost certainly living in a computer simulation. It follows that the belief that there is a significant chance that we will one day become posthumans who run ancestor-simulations is false, unless we are currently living in a simulation.
This is a modernized and somewhat gloomy brain in a jar scenario: more plausible, given its greater attachment to what we know about technology, and heavier on the existential angst. Either there is no golden future of humanity, or we're most likely participating in it already, but from inside the laboratory and cut off from that reality. Ghosts in the machine.
I've written on the topic of lazy immortality in the past, and the beliefs that attend it:
Wouldn't it be nice to wake up and find that we were all immortal? That would save a whole lot of work, uncertainty, and existential angst - and we humans are nothing if not motivated to do less work. The best of us toil endlessly in search of saving a few minutes here and a few minutes there. So it happens that there exist a range of metaphysical lines of thought - outside the bounds of theology - that suggest we humans are immortal. We should cast a suspicious eye upon any line of philosophy that would be extraordinarily convenient if true, human nature being what it is.
If you buy in to, say, the Many Worlds Interpretation of quantum mechanics (which a great many people in the field do) and you are fine with identifying your self as a specific pattern, no matter if there are discontinuities in the existence of that pattern, then you might argue that you are immortal.
If you ascribe a high level of probability to the belief that you are a simulated being, then you find yourself in an interesting position vis a vis your immortality or lack thereof - very similar to the position of theologians and believers, in fact. You may indeed be immortal in the pattern sense if those who run the simulation are ethical in ways that include not destroying sentient life if it could be saved without disrupting the experiment. Equally, depending on the nature of the computing hardware, you may be better thought of as less an individual and more a flitting sequence of briefly instantiated patterns, each having no relation at all to the last, running on different small pieces of a gargantuan machine. You are dead, briefly alive, dead again - over and again, millions of times a second. You are not alive and continuous in any way that I would recognize; no one small instantiation exists for long enough to even experience the coherent illusion that it is alive.
Or perhaps the plug will be pulled at some random time in the future and the simulation shut down, its data discarded. Or perhaps just your pattern won't be saved when your course in the simulation is run. Or perhaps the whole simulation was only started five minutes ago, our time, and so you are somewhat less old than you think you are. There are deeper rabbit holes to explore, but you might give pause to think that religious folk have it easier in one way at least: they've already been gifted with a rich history of theological argumentation and nonsense, and thus have no real need to work hard to make up any more of it.
The bottom line is that being a simulated being in someone else's simulation is pretty ugly from an existential point of view. In the real world, there's the possibility to bootstrap into the million year life span though advancing technology; not a giant possibility for any of us in middle age today, but it's not zero either. The members of a simulated world society could do all the right things and reach the same end goal - but they'd still be stuck in the simulation and at the mercy of its creators, so wouldn't have won anything approaching the same victory.
For all concepts of lazy immortality or variants on the brain in a jar, I think that the best course is to proceed as though what we see is what we get - assume we are in the real world, in these imperfect bodies, faced with real versions of these real challenges of aging and death. To do otherwise is to relinquish our potential, to lie back and relax whilst we are quite literally fighting for our lives:
Once upon a time, the planet was tyrannized by a giant dragon. The dragon stood taller than the largest cathedral, and it was covered with thick black scales. Its red eyes glowed with hate, and from its terrible jaws flowed an incessant stream of evil-smelling yellowish-green slime. It demanded from humankind a blood-curdling tribute: to satisfy its enormous appetite, ten thousand men and women had to be delivered every evening at the onset of dark to the foot of the mountain where the dragon-tyrant lived. Sometimes the dragon would devour these unfortunate souls upon arrival; sometimes again it would lock them up in the mountain where they would wither away for months or years before eventually being consumed.
Which is from the Fable of the Dragon-Tyrant, a mythologized view of the relationship between humanity and aging - also by Nick Bostrom. You should read it if you haven't already.